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Jul 2003
ISCV - Idle Speed Control Valve (idle speed control valve)
Operating principle
The rotary type ISCV valve is mounted on the throttle body and serves to bypass some of the air past the throttle valve to control the idle speed.
ISCV is controlled by an electronic control unit (ECU) with the possibility of feedback.
The ISCV is supplied with power through the main injection system relay, ground - through the ECU. There are two versions of rotary ISCVs: the old one with two controlled windings, the new one with one ECU controlled winding and the second permanently grounded winding. These types of ISCVs are not interchangeable, and you can determine which one is installed on the car according to the wiring diagram or wiring - on the old ones, two ISCV pins are connected to the computer, on the new one - one to the computer, the other to ground. 
Operation of ISCV with two windings
The valve contains two windings, a permanent magnet attached to the valve shaft and a locking element. A bimetallic spring is installed at the other end of the shaft, which allows you to control idling even if the electronic part of the ISC system fails. 
Mounted at the end of the shaft, a cylindrical permanent magnet rotates under the influence of an alternating magnetic field generated by coils T1 and T2. A locking element is installed in the middle part of the shaft, which opens or closes the bypass channel.
Each of the windings is connected to a transistor T1 or T2 in the ECU. When the transistor T1 is turned on, current flows through the winding, the resulting magnetic field causes the permanent magnet and the valve shaft to rotate clockwise. When the transistor T2 is turned on, the shaft rotates counterclockwise.
The control is carried out by changing the switching duration for each coil (signal duty cycle). The difference in the forces acting on the shaft determines the position of the valve. The signal frequency is 250 Hz.
Operation of ISCV with one winding
In valves of this type, the ECU sends a signal to only one of the windings, while the second is constantly on. Changing the degree of opening of the valve is also carried out by changing the duty cycle of the signal.
Bimetal spring
If the ISCV connector is disconnected or there is a problem with the electronics of the ISC system, the valve shaft is rotated into position by a bimetal temperature sensitive spring and held by a permanent magnet. In this case, the nominal idling speed is not reached on a cold engine and, conversely, too high revolutions occur on a warm one. The spring-set speed is 1000-1200 rpm (until normal operating temperature is reached).
Management in different modes
Engine starting
At start-up, the ECU opens the valve to the programmed position according to the coolant temperature and the measured RPM.
Engine warm-up
After starting, the ECU changes the idle speed according to the coolant temperature. As it warms up to normal operating temperature, the idle speed gradually decreases. In this case, the ECU compares the value of the current revolutions with the programmed ones.
Feedback
Feedback is carried out similarly to systems with a stepper motor. If the current speed is lower or higher than the programmed one, the ECU additionally opens or closes the valve.
Change in load or speed
To prevent erratic operation and too much load on the engine during a significant change in speed, the ECU monitors the signals of the start inhibit switch, air conditioner switches, headlights, rear window defroster, power steering pressure switch.
In accordance with the data received from them, the ECU changes the required speed, changing the position of the valve in advance and avoiding dips or jumps in speed.
The rotary ISCV system uses an adaptive control system. The ECU remembers and periodically updates the relationship between speed and control signal value, adjusting the ISC operating conditions as it wears out and is affected by other conditions. This data is stored in a volatile memory and after the battery is disconnected, a retraining procedure is performed.
The ECU memory contains the nominal values \u200b\u200bof the speed, which is maintained using ISCV. Feedback occurs at closed throttle and normal operating temperature. If the speed deviates from the programmed speed by more than 20 rpm, the ECU activates the ISCV and corrects it.
ISCV checks
Checking the operation of the valve.
Connect the wire from the positive battery terminal to the "+B" terminal, and from the negative terminal to the "RSC" and check that the valve closes.
Connect the wire from the positive battery terminal to the "+B" terminal and from the negative terminal to the "RSO" terminal and check that the valve opens. 
Vehicle check
Initial conditions:
- the engine is warmed up to normal operating temperature
- Rated idle speed adjusted correctly
- Gearbox - in neutral
- air conditioning off
A) Close the terminals TE1-E1 of the DLC1 connector (standard diagnostic connector in the engine compartment).
b) The idle speed should increase to 1000 rpm for 5 seconds and then return to nominal. Otherwise, check the valve and wiring.
c) Remove the jumper from DLC1.
Winding check.
a) Disconnect the valve connector
b) Measure the resistance between the +B and RSO/RSC terminals.
Rated resistance:
in the "cold" state (-10 - + 50С) - 17 - 24.5 Ohm
in the "hot" state (+50 - + 100С) - 21.5 - 28.5 Ohm
c) Connect the connector
P.S. In more modern systems, ISCVs are used, in which a magnet 3 rotates using a stepper motor 2. Through a worm gear 4, the rod 1 moves and the cross section of the bypass air channel changes (see photo below). Thus, the amount of air entering the cylinders and, as a result, the idle speed changes. This unit allows you to abandon complex adjustments, is easier to maintain, more reliable and, most importantly, allows you to accurately maintain the idle speed.
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Using a number of alflash materials
The most common and most widely repaired of Japanese engines is the (4,5,7)A-FE series engines. Even a novice mechanic, diagnostician knows about the possible problems of the engines of this series. I will try to highlight (collect into a single whole) the problems of these engines. There are not many of them, but they bring a lot of trouble to their owners.
Sensors.
Oxygen sensor - Lambda probe.
"Oxygen sensor" - used to detect oxygen in the exhaust gases. Its role is invaluable in the process of fuel correction. Read more about sensor problems in article.
Many owners turn to diagnostics for the reason increased fuel consumption. One of the reasons is a banal break in the heater in the oxygen sensor. The error is fixed by the control unit code number 21. The heater can be checked with a conventional tester on the sensor contacts (R- 14 Ohm). Fuel consumption increases due to the lack of fuel correction during warm-up. You will not succeed in restoring the heater - only replacing the sensor will help. The cost of a new sensor is high, and it makes no sense to install a used one (their operating time is large, so this is a lottery). In such a situation, as an alternative, no less reliable universal sensors NTK, Bosch or original Denso can be installed.
The quality of the sensors is not inferior to the original, and the price is much lower. The only problem may be the correct connection of the sensor leads. When the sensor sensitivity decreases, fuel consumption also increases (by 1-3 liters). The operability of the sensor is checked by an oscilloscope on the diagnostic connector block, or directly on the sensor chip (number of switching). The sensitivity drops when the sensor is poisoned (contaminated) with combustion products.
Engine temperature sensor.
"Temperature sensor" is used to register the temperature of the motor. If the sensor does not work correctly, the owner will have a lot of problems. If the measuring element of the sensor breaks, the control unit replaces the sensor readings and fixes its value by 80 degrees and fixes error 22. The engine, with such a malfunction, will operate normally, but only while the engine is warm. As soon as the engine cools down, it will be problematic to start it without doping, due to the short opening time of the injectors. There are frequent cases when the resistance of the sensor changes randomly when the engine is running at H.X. - the revolutions will float in this case. This defect is easy to fix on the scanner, observing the temperature reading. On a warm engine, it should be stable and not randomly change values from 20 to 100 degrees.
With such a defect in the sensor, a “black caustic exhaust” is possible, unstable operation on H.X. and, as a result, increased consumption, as well as the inability to start a warm engine. It will be possible to start the engine only after 10 minutes of sludge. If there is no complete confidence in the correct operation of the sensor, its readings can be replaced by including a 1 kΩ variable resistor or a constant 300 ohm resistor in its circuit for further verification. By changing the readings of the sensor, the change in speed at different temperatures is easily controlled.
Throttle position sensor.
The throttle position sensor tells the on-board computer what position the throttle is in.
A lot of cars went through the assembly disassembly procedure. These are the so-called "constructors". When removing the engine in the field and subsequent assembly, the sensors suffered, on which the engine is often leaned. When the TPS sensor breaks, the engine stops throttling normally. The engine bogs down when revving. The machine switches incorrectly. Error 41 is fixed by the control unit. When replacing a new sensor, it must be adjusted so that the control unit correctly sees the sign of X.X., with the gas pedal fully released (throttle closed). If there is no sign of idling, adequate X.X control will not be carried out, and there will be no forced idling mode during engine braking, which again will entail increased fuel consumption. On engines 4A, 7A, the sensor does not require adjustment, it is installed without the possibility of rotation-adjustment. However, in practice, there are frequent cases of bending the petal, which moves the sensor core. In this case, there is no sign of x / x. The correct position can be adjusted using a tester without using a scanner - on the basis of idling.
THROTTLE POSITION……0%
IDLE SIGNAL……………….ON
MAP absolute pressure sensor
The pressure sensor shows the computer the real vacuum in the manifold, according to its readings, the composition of the fuel mixture is formed.
This sensor is the most reliable of all installed on Japanese cars. His resilience is simply amazing. But it also has a lot of problems, mainly due to improper assembly. They either break the receiving “nipple”, and then seal any passage of air with glue, or violate the tightness of the inlet tube. With such a break, fuel consumption increases, the level of CO in the exhaust rises sharply up to 3%. It is very easy to observe the operation of the sensor on the scanner. The line INTAKE MANIFOLD shows the vacuum in the intake manifold, which is measured by the MAP sensor. If the wiring is broken, the ECU registers error 31. At the same time, the opening time of the injectors sharply increases to 3.5-5ms. When regassing, a black exhaust appears, the candles are planted, shaking appears on H.X. and stop the engine.
Knock sensor.
The sensor is installed to register detonation knocks (explosions) and indirectly serves as a "corrector" of the ignition timing.
The recording element of the sensor is a piezoelectric plate. In the event of a sensor malfunction, or a break in the wiring, at over 3.5-4 tons of revs, the ECU fixes error 52. Sluggishness is observed during acceleration. You can check the performance with an oscilloscope, or by measuring the resistance between the sensor output and the housing (if there is resistance, the sensor needs to be replaced).
crankshaft sensor.
The crankshaft sensor generates pulses, from which the computer calculates the speed of rotation of the engine crankshaft. This is the main sensor by which the entire operation of the motor is synchronized.
On 7A series engines, a crankshaft sensor is installed. A conventional inductive sensor is similar to the ABC sensor and is practically trouble-free in operation. But there are also confusions. With an interturn circuit inside the winding, the generation of pulses at a certain speed is disrupted. This manifests itself as a limitation of engine speed in the range of 3.5-4 tons of revolutions. A kind of cut-off, only at low speeds. It is quite difficult to detect an interturn circuit. The oscilloscope does not show a decrease in the amplitude of the pulses or a change in frequency (during acceleration), and it is rather difficult for a tester to notice changes in Ohm's shares. If you experience symptoms of speed limit at 3-4 thousand, simply replace the sensor with a known good one. In addition, a lot of trouble causes damage to the master ring, which mechanics break when replacing the front crankshaft oil seal or timing belt. Having broken the teeth of the crown, and restored them by welding, they achieve only a visible absence of damage. At the same time, the crankshaft position sensor ceases to adequately read information, the ignition timing begins to change randomly, which leads to loss of power, unstable engine operation and increased fuel consumption.
Injectors (nozzles).
Injectors are solenoid valves that inject pressurized fuel into the engine's intake manifold. Controls the operation of the injectors - the engine computer.
During many years of operation, the nozzles and needles of the injectors are covered with tar and gasoline dust. All this naturally interferes with the correct spray and reduces the performance of the nozzle. With severe pollution, a noticeable shaking of the engine is observed, fuel consumption increases. It is realistic to determine clogging by conducting a gas analysis; according to the readings of oxygen in the exhaust, one can judge the correctness of filling. A reading above one percent will indicate the need to flush the injectors (with the correct timing and normal fuel pressure). Or by installing the injectors on the stand, and checking the performance in tests, in comparison with the new injector. Nozzles are very effectively washed by Lavr, Vince, both on CIP machines and in ultrasound.
Idle valve.IAC
The valve is responsible for engine speed in all modes (warm-up, idling, load).
During operation, the valve petal becomes dirty and the stem is wedged. Turnovers hang on warming up or on X.X. (due to the wedge). Tests for changes in speed in scanners during diagnostics for this motor are not provided. The performance of the valve can be assessed by changing the readings of the temperature sensor. Enter the engine in the "cold" mode. Or, having removed the winding from the valve, twist the valve magnet with your hands. Jamming and wedge will be felt immediately. If it is impossible to easily dismantle the valve winding (for example, on the GE series), you can check its operability by connecting to one of the control outputs and measuring the duty cycle of the pulses, while simultaneously controlling the speed of X.X. and changing the load on the engine. On a fully warmed-up engine, the duty cycle is approximately 40%, by changing the load (including electrical consumers), an adequate increase in speed in response to a change in duty cycle can be estimated. When the valve is mechanically jammed, a smooth increase in the duty cycle occurs, which does not entail a change in the speed of H.X. You can restore work by cleaning soot and dirt with a carburetor cleaner with the winding removed. Further adjustment of the valve is to set the speed X.X. On a fully warmed up engine, by rotating the winding on the mounting bolts, they achieve tabular revolutions for this type of car (according to the tag on the hood). Having previously installed the jumper E1-TE1 in the diagnostic block. On the “younger” 4A, 7A engines, the valve has been changed. Instead of the usual two windings, a microcircuit was installed in the body of the valve winding. We changed the valve power supply and the color of the winding plastic (black). It is already pointless to measure the resistance of the windings at the terminals. The valve is supplied with power and a control signal of a rectangular shape with a variable duty cycle. To make it impossible to remove the winding, non-standard fasteners were installed. But the problem of the stem wedge remained. Now, if you clean it with an ordinary cleaner, the grease is washed out of the bearings (the further result is predictable, the same wedge, but already because of the bearing). It is necessary to completely dismantle the valve from the throttle body and then carefully flush the stem with the petal.
Ignition system. Candles.
A very large percentage of cars come to the service with problems in the ignition system. When operating on low-quality gasoline, spark plugs are the first to suffer. They are covered with a red coating (ferrosis). There will be no high-quality sparking with such candles. The engine will work intermittently, with gaps, fuel consumption increases, the level of CO in the exhaust rises. Sandblasting is not able to clean such candles. Only chemistry (silit for a couple of hours) or replacement will help. Another problem is the increase in clearance (simple wear). Drying of the rubber lugs of high-voltage wires, water that got in when washing the motor, provoke the formation of a conductive path on the rubber lugs.
Because of them, sparking will not be inside the cylinder, but outside it. With smooth throttling, the engine runs stably, and with a sharp one, it crushes. In this situation, it is necessary to replace both the candles and the wires at the same time. But sometimes (in the field), if replacement is impossible, you can solve the problem with an ordinary knife and a piece of emery stone (fine fraction). With a knife we cut off the conductive path in the wire, and with a stone we remove the strip from the ceramics of the candle. It should be noted that it is impossible to remove the rubber band from the wire, this will lead to the complete inoperability of the cylinder.
Another problem is related to the incorrect procedure for replacing candles. The wires are pulled out of the wells with force, tearing off the metal tip of the rein. With such a wire, misfiring and floating revolutions are observed. When diagnosing the ignition system, you should always check the performance of the ignition coil on the high-voltage arrester. The simplest test is to look at the spark gap on the spark gap with the engine running.
If the spark disappears or becomes filiform, this indicates an inter-turn short circuit in the coil or a problem in the high voltage wires. A wire break is checked with a resistance tester. A small wire is 2-3k, then a long 10-12k is further increased. The resistance of a closed coil can also be checked with a tester. The resistance of the secondary winding of the broken coil will be less than 12 kΩ.
Coils of the next generation (remote) do not suffer from such ailments (4A.7A), their failure is minimal. Proper cooling and wire thickness eliminated this problem.
Another problem is the current oil seal in the distributor. Oil, falling on the sensors, corrodes the insulation. And when exposed to high voltage, the slider is oxidized (covered with a green coating). The coal turns sour. All this leads to disruption of sparking. In motion, chaotic shootings are observed (into the intake manifold, into the muffler) and crushing.
Subtle faults
On modern 4A, 7A engines, the Japanese have changed the firmware of the control unit (apparently for faster engine warm-up). The change is that the engine reaches idle speed only at 85 degrees. The design of the engine cooling system was also changed. Now a small cooling circle intensively passes through the head of the block (not through the pipe behind the engine, as it was before). Of course, the cooling of the head has become more efficient, and the engine as a whole has become more efficient. But in winter, with such cooling during movement, the temperature of the engine reaches a temperature of 75-80 degrees. And as a result, constant warm-up revolutions (1100-1300), increased fuel consumption and nervousness of the owners. You can deal with this problem by either insulating the engine more, or by changing the resistance of the temperature sensor (deceiving the computer), or by replacing the thermostat for the winter with a higher opening temperature.
Oil
Owners pour oil into the engine indiscriminately, without thinking about the consequences. Few people understand that different types of oils are not compatible and, when mixed, form an insoluble porridge (coke), which leads to the complete destruction of the engine.
All this plasticine cannot be washed off with chemistry, it is cleaned only mechanically. It should be understood that if it is not known what type of old oil, then flushing should be used before changing. And more advice to the owners. Pay attention to the color of the oil dipstick handle. He is yellow. If the color of the oil in your engine is darker than the color of the pen, it's time to change instead of waiting for the virtual mileage recommended by the engine oil manufacturer.
Air filter.
The most inexpensive and easily accessible element is the air filter. Owners very often forget about replacing it, without thinking about the likely increase in fuel consumption. Often, due to a clogged filter, the combustion chamber is very heavily polluted with burnt oil deposits, valves and candles are heavily contaminated. When diagnosing, it can be erroneously assumed that the wear of the valve stem seals is to blame, but the root cause is a clogged air filter, which increases the vacuum in the intake manifold when contaminated. Of course, in this case, the caps will also have to be changed.
Some owners do not even notice that garage rodents live in the air filter housing. Which speaks of their complete disregard for the car.
The fuel filter also deserves attention. If it is not replaced in time (15-20 thousand mileage), the pump starts to work with overload, the pressure drops, and as a result, it becomes necessary to replace the pump. The plastic parts of the pump impeller and check valve wear out prematurely.
The pressure drops. It should be noted that the operation of the motor is possible at a pressure of up to 1.5 kg (with a standard 2.4-2.7 kg). At reduced pressure, there are constant shots into the intake manifold, the start is problematic (after). Significantly reduced traction. It is correct to check the pressure with a pressure gauge (access to the filter is not difficult). In the field, you can use the "return filling test". If, when the engine is running, less than one liter flows out of the gasoline return hose in 30 seconds, it can be judged that the pressure is low. You can use an ammeter to indirectly determine the performance of the pump. If the current consumed by the pump is less than 4 amperes, then the pressure is squandered. You can measure the current on the diagnostic block. 
When using a modern tool, the process of replacing the filter takes no more than half an hour. Previously, this took a lot of time. Mechanics always hoped in case they were lucky and the bottom fitting did not rust. But often that is what happened. I had to rack my brains for a long time, with which gas wrench to hook the rolled-up nut of the lower fitting. And sometimes the process of replacing the filter turned into a “movie show” with the removal of the tube leading to the filter. Today, no one is afraid to make this change.
Control block.
Until the year 98, control units did not have sufficiently serious problems during operation. The blocks had to be repaired only because of a hard polarity reversal. It is important to note that all conclusions of the control unit are signed. It is easy to find on the board the necessary sensor output to check or continuity of the wire. The parts are reliable and stable in operation at low temperatures.
In conclusion, I would like to dwell a little on gas distribution. Many “hands on” owners perform the belt replacement procedure on their own (although this is not correct, they cannot properly tighten the crankshaft pulley). Mechanics make a quality replacement within two hours (maximum). If the belt breaks, the valves do not meet the piston and fatal destruction of the engine does not occur. Everything is calculated to the smallest detail.
We tried to talk about the most common problems on the engines of this series. The engine is very simple and reliable, and subject to very tough operation on "water - iron gasoline" and dusty roads of our great and mighty Motherland and the "maybe" mentality of the owners. Having endured all the bullying, to this day he continues to delight with his reliable and stable work, having won the status of the most reliable Japanese engine.
Vladimir Bekrenev, Khabarovsk.
Andrey Fedorov, Novosibirsk.
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Cold start mechanism and IAC valve disassembly procedure
Immediately after starting, the speed rises to about 2000 rpm, but quickly drops to 1800 rpm, after a minute they are equal to about 1500 rpm (after which the XX valve begins to close) and slowly drop until the coolant warms up to 80 degrees (at this temperature, the XX valve must be completely closed, and the Lambda probe must be switched to operating mode).
Gasoline engines, as you know, have a quantitative regulation of the working mixture. The optimal mixture is considered to be in which 1 part of fuel falls on 14.7 parts of air, however, a highly enriched mixture is needed to start a cold engine. To enrich the mixture when starting injection engines, the so-called control air valve (IAC - Idle Air Control Valve or, as it is also called, By-Pass Air Control Valve / Solenoid) is used. The essence of his work is the formation of an air flow with a closed throttle. In the normal position, this valve is closed and opens only when the engine warms up to increase air flow (the air line of this valve goes into the intake manifold bypassing the throttle). And according to the increased air consumption (according to the data coming from the air flow meter or, as they say, the flow meter, or rather the MAF sensor - Mass AirFlow Sensor), the control unit (ECU) decides on an increased portion of fuel, which leads to an increase in speed to the heating level.
Thus, if the revolutions “float” when starting a cold engine, then most likely two are to blame: a clogged or failed IAC valve (and possibly an air line) or a MAF sensor.
Checking the IAC valve:
The IAC valve is located on the intake manifold on the right side of the vehicle, below the throttle position sensor (TPS - Trottle Position Sensor). It fits, respectively, an air hose and coolant hoses (the abbreviation I.A.C. of the same name is usually engraved directly on the plastic case of the solenoid, so it is impossible to confuse it!). If you do not have a tester at hand, then you can check the operation of this valve (very rudely!) Only by pulling off its connector at startup and making sure that the speed has dropped (and the engine has most likely stalled!). Do not forget that you can put the connector back only after turning off the ignition!
However, if the XX valve is completely "dead", then this will be shown by the car's computer self-diagnosis system. To correctly check the performance of the electromagnetic part of this valve, you must:
First, check the input voltage. To do this, on a cold engine, disconnect the connector, turn on the ignition (do not start the engine!) And make sure that there is a voltage of at least 10 volts on the connector (you need to look at the power wire - it is usually colored: yellow or red);
After that, we check the resistance between contacts 1 and 2, as well as between 2 and 3 of the valve itself. At a coolant temperature from -20 to +80 degrees, the resistance at the valve contacts should be in the range from 7.3 to 13 ohms (as a rule, its value is about 9 ohms);
Then we check if it "shorts" to the body - the resistance between each contact of the valve and the ground (car body) must be "infinite" (more than 1 megaohm);
And finally, it does not hurt to check this valve in operation. First, you need to make sure that the signal wire from the ECU is receiving the correct command. To do this, you need to find the signal wire (usually it is black or white) and make sure that 1 volt is present on it in the first minute after starting, and after one minute it changes to 10 volts. Otherwise, the ECU itself may be damaged.
After a voltage of 10 volts has come to the solenoid, the valve begins to close. In the future, the voltage may change in a small range (opening the valve to equalize XX on a hot engine) and the behavior of the XX valve during warm-up will be determined only by its mechanical part, which closes the air duct opening, depending on the temperature of the coolant supplied to it - in this case, the coil only creates necessary constant effort. After warming up to operating temperature, the IAC valve closes completely. At the same time, the usual Subaru revolutions of the twentieth should be set to about 750-800 rpm.
Checking the mechanical part of the valve can only be done after the engine has reached operating temperature. After a good warm-up (the coolant temperature arrow is in the middle position), you will need to turn off the engine, remove the valve and make sure that it is completely closed!
If you are convinced that the solenoid part of the XX valve is working properly and the ECU is giving the necessary signal, and idle on a cold engine continues to "jump", then you can try to check / clean the mechanical part of the IAC valve from carbon deposits and / or try to adjust its solenoid, by loosening the two mounting screws and carefully rotating the coil clockwise or counterclockwise by +/- 1 degree.
It is not necessary to immediately remove the IAC valve for cleaning, you can simply pull off the air hose and pour some solvent directly into the inlet (for example, aerosol brake cleaner or carburetor flushing fluid). After that, wait until the liquid dissolves the deposits, and then blow the air duct with a compressor. It would even be possible, having contrived, to pour such a liquid into the outlet located behind the throttle valve and repeat this operation several times on both sides. And at the same time it does not interfere with cleaning the deposits around the throttle valve in the throttle body. Just don't forget to blow out the duct with compressed air when you're done for extra cleaning and faster evaporation of the solvent.
However, if such a procedure does not help, then this valve will still have to be removed - first of all, in order to make sure that it closed after warming up, and also in order to carefully examine the mechanical part for possible breakdowns.
Here is the procedure for disassembling the IAC valve:
The IAC valve consists of two parts: a solenoid coil ("barrel" with a three-pin connector) that rotates the stem with the mechanical part of the valve located in a rectangular base, which is mounted on four bolts to the intake manifold. Three hoses are suitable for the base - air and coolant for heating the mechanical part of the valve.
Actually, it makes no sense to remove the solenoid itself (well, except perhaps to check the valve stem for play or to avoid damage when cleaning the mechanics): firstly, there is nothing to clean there, and secondly, you can “knock down” the setting (the coil can turn on the stem ). Therefore, if it has interfered with you in some way, and you certainly want to remove it, do not forget to remember the position relative to the fastening screws. You will have to set it again very carefully (+/- 1 degree, as mentioned above, can disrupt the operation of the engine during warm-up).
The valve itself must be removed very carefully so as not to damage its gasket (by the way, when replacing a failed valve, do not forget to replace it too). First you need to remove the hoses (air and coolant), unscrew the four bolts with a socket wrench, and then carefully disconnect the valve from the engine.
Now you can clean it with anything: the same aerosol solvent, carburetor cleaner or even washing powder in a basin. Just be sure to dry it thoroughly afterwards.
still hard to start:
In fact, the most common cause of problems when starting the engine can be a heavily contaminated air filter. If the outer surface of the filter element is frankly dirty, replace it immediately (for a simpler visual examination, such filters are specially painted in radical colors!). If it is just dusty, try blowing it from the inside.
Another, no less simple reason may be the usual depressurization of the intake tract. The "thrifty" Japanese usually use cheap clamps on all air tubes. And often the hoses just jump off (rarely burst). Therefore, carefully inspect the connections of all pipes (hoses, pipes, clamps, etc.) that go from the intake tract to other systems or elements of the car (this is the brake system, the adsorber canister, the PCV valve, and other forced crankcase ventilation hoses ). Particular attention should be paid to the tube that connects the fuel pressure regulator to the intake manifold.
If the air system is working, then you should proceed to check the fuel system. One reason for poor starting may be lean fuel mixture due to insufficient fuel pressure. There can be two reasons for this: it is either a "dying" fuel pump (which, however, usually performs a "farewell" song before its death), or a fuel pressure regulator. Sometimes the fuel pressure in the system can be increased by temporarily pinching the "return" hose (you should carefully pinch the excess fuel drain hose into the tank and do not keep it in this state after starting for more than 5-10 seconds, in order to avoid "flooding" of candles). If this operation helps, but the engine continues to stall, then you should not increase the time of pinching the hose, but it is better to repeat it several times until the engine warms up and stops stopping when you resume draining fuel.
The coolant temperature (coolant) sensor may also be the culprit for the problem of poor starting. And keep in mind that there are two such sensors: one serves to take readings for the temperature gauge on the instrument scale, and the other (ECT - Engine Coolant Temperature Sensor) takes readings for the control unit (ECU). Both of them are located on the right side under the intake manifold. If the first sensor "lies", then you will see it only on the instrument panel, but the readings of the second one can lead to much more serious consequences. To check the ECT sensor on all Subaru models, you need to disconnect its connector and measure the resistance of this sensor at different coolant temperatures: at 20 degrees it should produce 3.0 K ohms, at 50 - 0.7-1.0 K ohms, and at 80 degrees (normal coolant operating temperature) - 0.3-0.4 K ohm. If you have ever overheated the engine, then this temperature sensor should be carefully checked and, if possible, replaced. Otherwise, you will constantly have problems starting the engine, especially in cold weather. If you cannot check the serviceability of this sensor (the engine is not running!), then I advise you to take a variable resistor of 3-4 K ohms, connect it to the connector of this sensor and try to adjust the speed manually (based, for example, on the readings of the instrument cluster thermometer). scale and tachometer). Do not forget to turn off the ignition only after warming up and connect the standard coolant temperature sensor.
If it’s not the coolant temperature sensor, then you should check the candles (this is perhaps even a more important element than all the previous ones, but given the difficult access to them on boxer, and even more so turbocharged engines, I bring it at the end) . Visual inspection of the working part of the spark plugs can immediately show the state of the power system. If the insulator is clean and completely free of plaque, then this indicates a too lean mixture. This may also indicate that the candle is too hot, that is, heat is removed from the electrode too slowly. If this is the case, then you should replace the candle or adjust the composition of the mixture. If there are black (or very dark) deposits on the candle, the fuel mixture, on the contrary, is too rich, which means that not everything is in order with the ignition system on your car. If the plaque is black and oily, then this indicates engine wear and the need to check and repair it. And, finally, if the insulator is covered with a light brown coating without traces of breakdown, then the composition of the mixture is optimal and the engine is in good condition. And red terry deposits with characteristic traces of a breakdown indicate that you "got" on gasoline with an "excessive" content of additives that increase the octane number. Most often, in such cases, it is enough to replace the candles and the engine starts to normal.
If none of the above manipulations helped, remove the ECU diagnostic codes and proceed to check all the elements of the injection system one by one:
Wiring;
All gaskets are perforated by air;
Injection system relay;
fuel injectors;
ignition coils;
output ignition unit;
pressure sensor;
Speed sensor;
crankshaft sensor;
And finally, the control unit itself (ECU - Engine Control Unit)
If there are serviceable elements of the injection system, there are no problems with cold start on Subaru cars!
1. Set the parking brake, support the wheels of the car with wheel chocks and shift the transmission to neutral gear (manual transmission) or to the “P” (AT) position. Connect a tachometer to the engine according to the manufacturers instructions. Start the engine and raise its speed to 3000 rpm. Wait for the cooling fan to operate, then reset to idle and record the tachometer readings (the cooling fan and all electrical consumers must be turned off). If the crankshaft speed is 650 ÷ 700 rpm, then the system is functioning properly. If the measurement is below 650 rpm, disconnect the IAC valve electrical connector. When the valve is disconnected, a noticeable decrease in engine speed should occur, otherwise the valve is most likely defective. If there is a drop in speed, and the problem with maintaining their stability does not disappear, check the condition of the wiring harness and its contact connections in the area between the IAC valve and the PCM.
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2. If the tachometer reads more than 750 rpm, stop the engine and disconnect the intake duct from the throttle body. Run the engine to idle. Shut off the lower port of the throttle body (connected to the IAC valve) with your finger - if the speed drops noticeably, adjust the setting of their idle value, bringing it in line with the requirements of the Specifications (see Chapter Settings and Routine Maintenance). If the adjustment fails, replace the IAC valve. If there is no drop in speed, check the intake tract for signs of vacuum loss.
3. If the test confirms that the IAC valve is working, however, the problem with the violation of the stability of the revolutions remains, check the condition of the electrical wiring and its contact connections in the area between the valve and the PCM.
5. Using an ohmmeter, measure the resistance between terminal 1 of the IAC valve and ground. The device must register the presence of conductivity, otherwise, carry out a ground repair.
6. If the results of both checks are positive, drive the car for more detailed diagnostics to a service station.
So, what are the most common problems when the engine is idling? Experts identify two of the most common malfunctions. Foreign experts call the first of them the aviation term - "surging". This term refers to any sudden changes in speed up or down. Sometimes this problem occurs after heavy braking, but it is equally rare that a sharp decrease in speed occurs during normal parking, up to a complete stop of the engine. In other words, this is a whole group of problems that can be caused by a variety of reasons.
The second problem is idle instability, in which the engine speed slowly changes in the direction of increase and decrease.
The list of possible causes that cause these problems can be very wide.
Here are just the most common ones:
The transmission lock does not lock the automatic transmission lever
Air leak
EGR valve stuck open
Dirty and sticky IAC valve, which is responsible for regulating the working mixture (P0505)
Incorrect operation or breakdown of the engine temperature sensor
knock sensor problem
EGR channel contamination
Clogging of the variable valve timing system
Air in the cooling system
The MAF connector has an unstable connection, or the MAF sensor itself is not working correctly
Problems with pressure in the fuel system
Clogged fuel filter
Clogged or clogged exhaust system
Inoperative crankshaft position sensor (P0336)
Open in power steering sensor circuit
Constant turning on / off of the air conditioner due to low refrigerant level
Throttle Position Sensor (TPS) Malfunction
Clogged catalytic converter
Misfire
Incorrect operation of the PCV valve (exhaust ventilation
High oil pressure in the system (in diesel engines).
So, there are a lot of reasons, and it would not hurt us to systematize the information and highlight the most likely sources of malfunction. It is on them that you should pay attention first of all when diagnosing an engine.
Problem:
A sharp fluctuation in the idle speed of the crankshaft.
What are we checking?
1. Fuel pump control circuit.
2. Spark plugs.
3. Ignition stability.
4. The condition of the injectors.
5. Blocking the automatic transmission lock.
Problem:
High idle.
What are we checking?
4. PCV valve
Problem:
Low idle.
What we check:
2. The power circuit of the engine control unit (ECM).
3. Air conditioner control circuit.
4. PCV valve.
5. The condition of the injectors.
Problem:
Floating idle.
What are we checking?
2. Engine control unit (ECM).
3. PCV valve.
4. Fuel pump control circuit.
5. Spark plugs.
6. Stability of the ignition system.
7. The condition of the injectors.
Now let's look at each of these points in detail.
Faulty crankshaft position sensor
As a rule, a malfunction of the crankshaft position sensor is accompanied by a P0336 code. Many engines use a two-wire sensor with a signal wire and ground as the crankshaft position sensor. The sensor has a permanent magnet or a three-wire Hall sensor, which is installed in the engine block coaxially with the gear wheel mounted on the crankshaft. During the rotation of the wheel, the magnet generates an alternating current signal, transmits it to the control unit, which determines the engine speed from this signal.
Depending on the engine design and model, the number of teeth on the crankshaft sprocket may vary. Keep in mind that even within the same engine family (GM LS for example) the number of teeth can vary. Accordingly, the installation of sprockets with a different number of teeth is not permissible.
The crankshaft position sensor, as well as the signals from the camshaft position sensor, are used by the engine control unit to regulate fuel injection and spark supply. Naturally, any error in the readings of the sensor can easily cause a misfire, which leads to sudden and short idle dips (which many car owners describe as engine shaking). In addition, incorrect readings from the crankshaft position sensor can cause the engine to fail to start or cause the engine to stop idling intermittently. The distortion of the indicators of the crankshaft position sensor is quite often associated with a malfunction of the sprocket: wear or breakage of the teeth, plaque of metal particles on the teeth, and so on. In addition, a fairly common cause of sensor malfunction is a wiring fault. On most engines, the sprocket is pressed onto the crankshaft, but during operation it can loosen and come out of its seat. This does not happen often, however, if such a suspicion arose, it must be immediately checked and, if detected, eliminated, since the free rotation of the sprocket on the crankshaft can cause not only misfires, but also mechanical damage inside the engine - damage to the cylinder block or piston skirt. If this problem is identified, do not try to replace the crankshaft sprocket yourself. Most often, this requires a special dealer tool and diagnostic equipment. It is best to send such a car to a dealership or replace the entire crankshaft, along with the installed sprocket.
Faulty pressure sensor in the power steering hydraulic system
One of the cars in which this problem occurs most often is the Honda Odyssey. The sensor wire is corroded. The result of this is an unstable signal, which the engine ECU perceives as the active operation of the hydraulic booster in a situation where it is stationary. The control unit begins to regulate the engine speed, and the tachometer grid begins to scour. The problem is solved by replacing the wiring.
Air in the cooling system
In order for the coolant temperature sensor to show the correct temperature, it must be constantly immersed in the liquid. In the event that there are air pockets in the system, there is a possibility that hot air can get on the sensitive element of the sensor and lead to temperature fluctuations. In turn, the engine control unit (ECU) will begin to change the composition of the fuel-air mixture in order to adapt to the “change” in the operation of the engine. Make sure the cooling system is full and remove the air lock.
Problems with the throttle position sensor
If the throttle actuator shaft is worn, check the location of the TPS throttle sensor. It should be at the very end of the shaft. Any deflection of the throttle actuator shaft caused by wear will affect the signal generated by the throttle position sensor. The ECU can interpret this as a real change in throttle position. In accordance with this, the control unit will give a signal to increase the fuel supply, which will lead to a re-enrichment of the fuel mixture. A similar problem occurs in the event of a sensor breakdown or a power failure, poor contact. You can check the performance of the sensor as follows. Stop the engine (key to the OFF position), connect a multimeter to the sensor and measure the voltage with the accelerator pedal released. Then press the accelerator several times and check the change in voltage. If after this the voltage readings change, then check the condition of the throttle shaft and the wiring of the TPS sensor.
Air Control Valve (IAC) Malfunction
To enrich the mixture when starting injection engines, the so-called control air valve (IAC - Idle Air Control Valve or, as it is also called, By-Pass Air Control Valve / Solenoid, AIS (Automatic Idle Speed), ISC (Idle Speed Control) is used ). The essence of its work is the formation of air flow when the throttle is closed. In the normal position, this valve is closed and opens only when the engine warms up to increase air consumption (the air line of this valve goes into the intake manifold bypassing the throttle). As a rule, when an problems with the IAC valve, the engine block generates an error code P0505. In this case, the engine may behave differently: stalls at idle, or, conversely, increases speed. To actuate the valve, a plunger mechanism is used, which, in the event of clogging, has a tendency to jam or stick in open position This is not uncommon as the valve tends to accumulate carbon deposits. In addition, the IAC valve is equipped with a vacuum hose. If this hose is micro-cracked or otherwise damaged, the engine will react as if the IAC is bad. Some Toyota and Lexus engines have IAC solenoid valves that require periodic cleaning.
To check the IAC, clear all errors in the control unit, turn off the valve and start the engine. If the error code P0505 no longer appears, then the IAC valve is not working. If the error code reappears, this means the likelihood of a short circuit or other wiring problems. Check the wiring harness all the way to the ECU.
Here is one example of diagnosing the air control valve control system on a 2008 Toyota Yaris with a 1NZ-FE engine. The control unit issues code P0505.
Description of the control system
The idle speed on this vehicle is controlled by ETCS (Electronic Throttle Control System). The system will consist of:
throttle body,
Throttle drive, which is responsible for opening and closing the damper,
Throttle position sensor (TPS), which detects the throttle valve opening angle,
Accelerator Pedal Position Sensor (APP),
The engine control unit, which controls the operation of all components.
The engine control unit controls the idle speed and the amount of incoming air at idle according to ISC (Iddle Speed Control). The system generates an error if:
The idle air volume is fixed at the maximum or minimum level at least 5 times per trip,
After a trip at a speed of 10 kilometers per hour or more, the actual idle speed deviates from the nominal by 100 or more rpm at least 5 times per trip,
In the cases described above, on the instrument panel, the signal lamp lights up, and error P0505 is recorded in the control unit. There are several other reasons for this error:
The passenger compartment carpet creates a slight pressure on the gas pedal, as a result of which the throttle valve is always in a slightly ajar position,
The accelerator pedal cannot be fully released.
Merry M.A.F.
A malfunctioning MAF sensor causes sudden changes in engine speed - from 0 to 2,000 rpm. Most often, the problem occurs due to an open or short circuit in the wire bundle, or due to damage (clogging) of the MAF sensor.
The MAF sensor measures the amount of air passing through the throttle body. The ECU uses this information to determine the fuel injection timing and create the optimum air/fuel mixture. Inside the sensor there is a heated sensitive element made of platinum wire through which air flows. The wire is heated to a certain temperature using a current of a certain strength. The incoming air cools the wire, changing its resistance. To keep the current reading constant, the engine ECU changes the voltage on the MAF wire. This voltage is proportional to the volume of air passing through the sensor. This is how the engine control unit calculates the volume of incoming air.
Accordingly, if there is a defect in the sensor (open or short circuit in the MAF circuit), the voltage level deviates from the normal operating range. The ECU interprets this as a malfunction in the MAF and sets a Diagnostic Trouble Code (DTC).
MAF fault codes:
P0101: Indicates high voltage (engine rpm is below 2000 rpm, coolant temperature is 158 degrees F or higher, and MAF output voltage is greater than 2.2 V), or low voltage (engine rpm is greater than 3000 rpm and MAF output voltage is less than than 0.93 V).
P0102: The MAF circuit has a low input voltage (less than 0.2V). The error appears in the event of an open circuit in the electrical circuit for more than 3 seconds. The error may also indicate a malfunction of the MAF or severe contamination of the sensor. If you use so-called impregnated air filters in your car, they can cause this malfunction.
P0103: MAF input voltage high (more than 4.9 V). This usually means a short circuit in the sensor circuit. MAF may be damaged.
P0104: MAF circuit open (poor contact quality, worn connectors, contacts or wires). This code may also indicate an air leak.
Diesel vibrations
Diesel engines (take the Ford 7.3L and 6.0L as an example) typically have a high pressure oil system that controls the fuel injectors. High pressure readings at idle are typically 500 psi. At 3300 rpm the pressure is 120 psi and at full load it is 3600 psi.
The system consists of a high pressure oil pump and an injection pressure regulator. Fluctuating idle speed may occur in case of wear or wedging of the idle speed controller. In some cases, there is also a complete stop of the engine when driving at low speeds. Many owners of diesel cars know the problem when the diesel engine stalls at the moment of stopping at a traffic light, after moving the automatic transmission knob to the N or P position, it starts again, but again at the next traffic light it stalls. This is one of the signs of a worn idle speed control. Other symptoms:
difficult start,
Small dips when you sharply press the accelerator pedal.
Of course, such symptoms can indicate a variety of malfunctions, but first of all, the high oil pressure system should be checked. The first reaction of the owner, faced with this problem, is that moisture got into the fuel filter and it needs to be replaced. Of course, for a diesel engine that operates in cold climates, this procedure will not be superfluous. You should always start small. But if changing the filters did not solve the problem, then you should check the valve of the high oil pressure system and the idle speed control. The system operates at very high pressure and any deviation in readings will cause the engine control unit to start changing its settings for the formation of the fuel-air mixture, which will most likely lead to its over-richness.
Note: Don't rush to throw away the sticky high pressure valve and buy a new one. Most of them are quite repairable. All repairs come down to disassembling the valve, cleaning it and reassembling it. Also remember to measure the oil pressure in the high pressure rail and check it for oil stains, which not only quickly foul the engine at the rear of the intake manifold, but can also cause a pressure drop in the system. It is also important to remind customers that only certain grades of engine oil should be used in diesel engines. So, in order to maintain the correct and constant pressure to the fuel injectors in modern engines, it is necessary to use oils with special anti-foam additives that do not allow oil aeration. According to API, such oils have a CF-4 / SH or CG-4 / SH class or higher. These additives develop their resource in about 5-8 thousand kilometers, so the oil must be changed in a timely manner.
