High revs at idle Aveo. High idle - what could be the reason? Ways to solve problems

24.08.2020

Which is necessary to maintain the process of combustion of fuel in the cylinders at a minimum level, that is, so that the engine continues to work and does not stall. On different motors, the idle speed may vary, and also depend on the temperature of the internal combustion engine. In the case of an increase in the specified speed XX, the engine begins to consume more fuel, the exhaust in this mode becomes more toxic. A decrease in idle speed leads to unstable operation of the power unit, as well as to the fact that the engine starts to stall after releasing the gas pedal. In this article we will talk about what could be the reason for high idle engine speeds, why high idle speeds on a warm engine are found on many cars, and also consider the main ways to diagnose this malfunction.

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High idle engine speed: injector

The speed and operation of the motor at idle actually means that air is supplied to the engine bypassing the throttle. In other words, at idle, the indicated damper is closed. Note that normal idling for different units is about 650-950 rpm. In parallel with this, a frequent malfunction is that on a warm engine, the XX speed is kept at about 1500 rpm and above. This indicator is a sign of a malfunction that should be fixed.

It should also be noted such a phenomenon when the idle speed “floats”, that is, for example, it rises to 1800 rpm, after which it drops to 750 and rises again. Very often, increased idle speed and floating speed are the result of the same breakdowns. Let's take a look at an injector petrol unit as an example. In such an internal combustion engine, engine speed depends on the amount of intake air. It turns out that the more the throttle valve opens, the more air enters the intake manifold. Then it determines the amount of incoming air, simultaneously takes into account the throttle opening angle (throttle position) and a number of other parameters, after which it delivers the appropriate amount of gasoline.

If the ECU does not have accurate information about the amount of air due to malfunctions, then the following will happen: the controller will first increase the speed, enriching the mixture (more fuel is supplied). Then, with this amount of fuel and an additional volume of air that the ECU does not know about, the mixture will become leaner, and the engine will begin to run erratically or may almost stall. In other words, revs will start to drop when the mixture is too lean. A decrease in speed means that the amount of air taken in by the unit is also reduced. At a certain point, the composition of the mixture (the ratio of fuel and air) will again be optimal, as a result of which the speed will rise again and then begin to fall or “float”. The reason for this operation of the internal combustion engine may be a failed or intermittent operation,. You should also take into account the possible air leakage at the inlet.

Another case is when the engine keeps the idle speed around 1500-1900 rpm, while running smoothly, the speed does not float. In this case, it can be assumed that the injector delivers so much fuel in idle mode that it is enough to operate at such high speeds. In other words, there is an overrun of fuel. These features may be typical for some engines and absent on others, since there is a dependence on the device of a particular injection system (units with an air flow meter, engines with a pressure sensor in the intake manifold). It is obvious that air leakage is a common cause of an increase in engine speed or floating speed at idle.

Now let's figure out where the excess air can enter the intake. You should look for a problem in four main directions:

throttle valve;
channel XX;
a device for maintaining "warm-up" revolutions;
servo motor for forced increase in revolutions XX;

As for the first case, the throttle is controlled by the gas pedal. At idle, the engine should run without pressing the accelerator. It should be borne in mind that on many cars the gas pedal is mechanical, that is, it is connected to the damper opening mechanism with a conventional cable. If this cable is soured, broken or overtightened, and there are also problems with the mechanism itself, then the banal effect of pressing the gas pedal may occur. In this case, the engine will keep the increased speed, as the ECU thinks that the driver is pressing the accelerator and the damper is slightly ajar.

In the second case, excess air can pass through the idle channel. Such a channel is available on the vast majority of injection internal combustion engines. The specified air channel bypasses the throttle and is called the idle channel. In the implementation of the circuit there is a special adjusting screw. Using this screw, you can change the cross section of the channel, thereby increasing or decreasing the amount of air entering the motor and adjusting the idle speed.

Another place where air leakage is possible is a device that maintains increased idle speeds while the engine is warming up. Simply put, there is a separate air channel in which there is a solution for closing it after the motor warms up (rod or damper). In the device for overlapping there is a sensitive thermoelement. On many units, the specified element interacts with antifreeze in, similarly. On a hot motor, the device operates in such a way that the stem extends completely or the damper rotates to such an angle as to completely block the channel for supplying additional air.

As a result, the ECU calculates the amount of air, reduces the amount of fuel supplied and the speed drops. If the motor is cold, this channel is initially open. In this case, the ECU receives readings from the temperature sensor and enriches the fuel mixture. Problems with revolutions can occur both as a result of the failure of this device, and after failures in the operation of the temperature sensor.

The list is completed by a special servo device - the idle speed controller, which is installed in a separate air channel. This solution is capable of forcibly increasing idle speed. In various circuits, this may be an electric motor, a solenoid, a variant of a solenoid valve, etc. The main task of such a regulator is to ensure a smooth transition of the engine to the XX mode after releasing the gas pedal. In other words, the engine does not decelerate abruptly after closing the throttle, but gradually. Another function of the device is to increase the idle speed at the time of starting the engine, and then smoothly reduce them to the required ones. Also, the regulator raises the speed after an increase in the load on the internal combustion engine in idling mode (turning on the air conditioning system, heated seats or mirrors, high or low beam headlights, parking lights, etc.). The failure of this device will naturally lead to an increase or floating in idle speed.

Increased speed XX on engines with a carburetor

At the very beginning, we note that an increase in the XX speed on carburetor engines is often associated with the metering device itself. If high idle engine speeds are noted in the case of a carburetor engine, then there may be several reasons.

The first reason is a knocked down idle adjustment. Such adjustment is carried out using an adjusting screw, which allows you to enrich or deplete the mixture. To solve the problem, you should correctly adjust the idle speed on the carburetor.
You should also pay attention to the fact that the air damper may not fully open on carbureted cars.
Another place to pay attention to is the shutter of the first chamber in the carburetor. The indicated damper may not close completely due to defects in the damper itself or an incorrectly adjusted actuator.
Finally, we add that a noticeable increase in the fuel level can be observed in the carburetor float chamber, which also leads to an increase in idle speed.

What is the result

It should be noted that the problem of idling on an engine with an injector is diagnosed by checking the main systems that are responsible for the intake of air into the internal combustion engine, as well as changing the composition of the mixture, taking into account the amount of incoming air. It turns out that it should be taken into account that the failure of individual ECM sensors can lead to an increase or floating speed of the XX.

In the general list of the main reasons why idle speed can increase at the injector, there are: idle speed controller, TPS, power unit temperature sensor, problems with the throttle opening control mechanism, intake air leakage. We add that before in-depth diagnostics, you should first carry out the throttle cleaning procedure, since a dirty throttle is a common cause of increased speed or unstable idling of the engine.

High idle engine due to air leakage and vacuum line leakage

So, if the cause of high idle was excessive air entering the engine, then here the first thing to check is the throttle cable. Because of it, the damper may remain too open at idle, as a result of which the latter grow. This happens because the "brains" of the engine see that a lot of air (more precisely, oxygen) enters the manifold, and therefore correct the fuel supply, increasing it. As a result, the engine speed increases at idle. Cleaning the throttle body with special chemicals can help in this case.

More air can also enter the manifold due to a leak in the air intake system. In this case, all vacuum lines, head breathers and all sections of the air flow line to the engine should be checked for air suction. Listen for hissing sounds, which can be a key indicator of vacuum leaks and air leaks.

High idle due to problems in the ignition system

In this case, the reason lies in one of the details of the ignition system - also a fairly common cause of a problem with speed. Here you should check and, if necessary, replace the distributor cap, ignition wires or elementary spark plugs.

Other causes of increased idle speed and solutions:

idle sensor. In principle, this malfunction should be included in the list of common ...
Fuel pressure control can operate at too low a pressure. Check the fuel pressure with a special fuel pressure gauge. Replace the fuel pressure regulator if necessary (not a do-it-yourself job for many drivers).
Incorrectly installed or knocked down ignition timing(in this case, usually idle speed does not increase much).
The reason may be malfunction in the computerized control system engine. Errors should be read with a diagnostic tool to identify the problem.
Generator also sometimes causes high idle. If it doesn't work properly and doesn't generate enough current, then the motor will try to spin it even harder to balance the voltage.
If you know what it looks like and where it is PCV valve and its hose then check them out. Using pliers, pinch the hose of this valve. The engine speed should drop slightly. If this does not happen, then the faulty valve is the cause of the increased engine speed - it needs to be replaced.
Overheating of the engine or a defective engine temperature sensor can in rare cases also cause high idle speeds.

I began to receive letters in the mail with the problem of high speed when starting the engine. Immediately, the arrow rises to about 3,000 and after a few seconds falls to its normal position. Let's reason logically. Why do we depend on engine speed? RPM is directly related to the throttle opening angle. The larger the angle it is open, the greater the engine speed. Whoever has a BC, the easier it is, they can simply look at the IAC readings and determine if it is the case. Those who do not have BC will need the help of a friend. You need to put him in the driver's seat, and open the hood yourself and watch the metal lever connected to the throttle axis (located in the center of the plastic washer on which the gas cable is attached). You can watch the video on the page:. This lever is fully connected to the IAC - idle speed control. Ask a friend to turn on the ignition. The lever should move to the left, opening the damper to start. The amount of deviation will depend on the engine temperature. If, after starting, the lever deviated even more to the left, thereby opening the damper more, just by 3,000 rpm, and when the speed drops, the lever will be closed along with the damper, then the matter is in the IAC. Turnovers correspond to the position of the remote control.

Let's look at another option. Let's say we have a good IAC. What could cause the revs to go up? I often go to the forums, see what new sores pop up on our machines. And there is a misconception. The question is: "Why low speed?". And in the answers they write that you need to look at all the hoses, if there are any cracks and if there is any air leakage. They write correctly, but only for cars with DMRV - Mass Air Flow Sensor. This sensor is placed after the air filter and takes into account the air flow passing through it. And the air leak comes after him, and he is not able to determine this. It turns out that more air passes into the engine, and the mixture becomes lean, which leads to a decrease in speed.
. . With us, it's the other way around. It costs DBP, and it determines the absolute pressure in the intake manifold. If there is a leak of air, then he will catch it. It turns out that the damper passes its portion of air, and the suction still adds its own. DBP takes everything into account, and the turnover increases. And in any case, the nozzles inject as much gasoline as necessary for the engine to work properly. This is a plus for us. Soon the ECU will realize that the speed is too high and will give a command to the IAC to cover the DZ - throttle, and everything will settle down. The next time you start it should do it again. Now let's think about where extra air can come from, except for bursting hoses. Three systems come to mind, although even 4.

If the piston is jammed or the spring in the crankcase exhaust valve pcv bursts, then the air will simply be sucked, bypassing the damper, through a long hose, through the valve cover, through the faulty valve into the air manifold.
. . If the EGR valve of the exhaust gas recirculation system is not working, the gases will also go into the air manifold through a metal tube. It is better to turn off the EGR valve immediately:.
. . If the adsorber purge valve is not working, then gasoline vapors will also go through the tube to the manifold.
. . And the last system that is connected to the air manifold is a system for changing its length. To the right of the collector is the actuator itself, black plastic, similar to a mushroom cap. It has a fitting on top, and a black tube is connected to it through a rubber tip. Another tube of this system is connected to the air manifold itself. This mechanism itself has a membrane - a diaphragm, and if it is torn, then air will flow through these tubes into the manifold until the engine exceeds 4,000 revolutions. And then just switch to a short collector and block this circle. Tomorrow is Monday, I'll go to work. I think there will be free time for the experiment. I have a lot of plugs on the intake manifold fittings, and even different diameters. We will simulate air leakage and see how the engine behaves. Then we will know for sure whether our theoretical conclusions and the logical chain are correct. OK, see you tomorrow. I think in the evening by 10 o'clock I will post the video on the blog and on YouTube.
. . Well, everything is ready.