Chevrolet Lacetti idle speed fluctuates. High engine speeds of the Chevrolet Lacetti jump engine speeds

I started receiving letters in the mail about the problem of high speeds when starting the engine. Immediately the needle rises to about 3,000 and after a few seconds drops to its normal position. Let's think logically. Why does our engine speed depend? The revolutions directly depend on the opening angle throttle valve. The greater the angle it is open, the higher the engine speed. For those who have a BC, it’s even easier; they can simply look at the IAC readings and determine whether it’s the problem. Those who don’t have a bookmaker will need the help of a friend. You need to put him in the driver's seat, 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 throttle cable is attached). You can watch the video on the page: . This lever is completely connected to the IAC - idle air control. Ask a friend to turn on the ignition. The lever should move to the left, opening the damper slightly to start. The amount of deviation will depend on the engine temperature. If, after starting, the lever deviates even more to the left, thereby opening the damper more, just at 3,000 rpm, and when the speed drops, the lever and the damper close, then the problem is the IAC. The revolutions correspond to the position of the remote control.

Let's look at another option. Let's say our IAC is working properly. What could cause the revs to rise? I often go to forums to see what new problems are popping up on our machines. And there is a wrong opinion there. The question is: “Why low revolutions?” And in the answers they write that you need to look at all the hoses to see if there are any cracks or air leaks. They write correctly, but only for cars with a mass air flow sensor - sensor Mass Flow Air. This sensor is installed after air filter and takes into account the air flow passing through it. But the air leak comes after it, and he is not able to determine it. It turns out that more air passes into the engine, and the mixture becomes leaner, which leads to a decrease in speed.
. . With us it’s the other way around. It stands for DBP, and it determines the absolute pressure in the intake manifold. If there is an air leak, it will catch it too. It turns out that the damper lets in its portion of air, and the suction also adds its own. DBP takes everything into account, and the speed increases. And in any case, the injectors inject as much gasoline as needed for proper operation engine. This is a plus for us. Soon the ECU will understand that the speed is too high and will give a command to the IAC to cover the throttle valve, and everything will settle down. The next time you start it should happen again. Now let's think about where the excess air could come from, other than burst hoses. Three systems come to mind, although even 4.

If the piston is jammed or the spring in the PCV valve (crankcase gas exhaust) is broken, 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 faulty, then the gases will also flow into the air manifold through a metal tube. It is better to turn off the EGR valve immediately: .
. . If the adsorber purge valve is faulty, then gasoline vapors will also flow through the tube into 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 rpm. And then it will simply switch to a short collector and block this circle. Tomorrow is Monday, I'll go to work. I think there will be free time to conduct an experiment. I have a lot of plugs on the intake manifold fittings, and even of different diameters. We will simulate air leaks and see how the engine behaves. Then we will know for sure whether our theoretical conclusions and logical chain are correct. Okay, see you tomorrow. I think by 10 o’clock in the evening I’ll post the video on both the blog and YouTube.
. . Well, everything is ready.

Many car enthusiasts have come across the concept of floating speed at idling engine. For Lacetti, as practice shows, this is frequent malfunction, which you can fix with your own hands, but sometimes you will need to use a car service.

Possible faults

After talking with car owners, as well as with car service technicians, we can conclude that floating engine speed on a car is a fairly common effect. Most car enthusiasts assure that this malfunction appears during warranty service. This may be due to many factors.

Let's consider the main reasons for the occurrence of floating engine speeds:

• Fuel system malfunction.
• Ignition problems.
• ECU errors.
• Poor quality fuel.

All these reasons contribute to the appearance of such an effect. The most common reason is problems with injection.

Repair methods

Before we move on to fixing the problem, it is worth noting that floating speed is just the beginning, since failure to correct the problem in a timely manner can lead to a “start-stall” effect. So, let's consider the sequence of actions to eliminate the causes of floating engine speed.

Fuel system

As practice and experience show, floating speeds appear in the event of an uneven supply of fuel to the combustion chambers, or constant change amount of fuel mixture. First of all, this is due to the injectors, which may be dirty. At the same time, this may not be felt when moving, but when idle speed The tachometer will immediately show this. Therefore, it is necessary to dismantle and check the injectors on a special stand.

Also, the malfunction may be caused by a breakdown of the gasoline pump, which does not supply fuel evenly or is clogged fuel filter. If necessary, you need to replace the filter element and check the fuel pump.

A change in the amount of fuel mixture may be due to a clogged throttle or worn air filter. Therefore, the filter element is changed and the throttle valve must be cleaned.

Ignition problems

Problems with idle speed may occur due to incorrect operation of the ignition system. Namely, it may be related to the lock or wiring. So, it is worth checking and, if necessary, replacing damaged elements. It is best to change the ignition switch assembly and test the wires that go from it to ensure they are working properly.

ECU errors

Often, a car malfunction is associated with errors in the electronic control unit, as well as a malfunction of the controllers on the board. Of course, another reason could be the firmware that is out of order. Many car enthusiasts change operating system, but this doesn't always help.

As practice shows, an ECU malfunction can pose a problem for the performance of many systems. Therefore, if the fault cannot be eliminated using the previous methods, it is necessary to replace the control unit.

Poor quality fuel

In many cases, poor quality of fuel poured into the vehicle tank can cause clogging of the fuel pipeline and injection system, which in turn gives the effect of uneven fuel supply. To eliminate the malfunction, you should drain the old fuel, clean fuel system and fill in with new high-quality gasoline.

Conclusion

Floating engine idle speed Chevrolet Lacetti, may lead to other, more serious problems. So, if such an effect occurs, it is necessary to find the cause and eliminate it. If you can’t do it yourself, you need to contact a car service, where they will quickly find and fix the problem. Repeatedly, due to the constant effect of floating speed, car owners had to electronic unit management.

My Chevrolet Lacetti, how I got rid of the effect of floating engine speed.

The ECU determines the value of this angle by the voltage of the second variable potentiometer PDZ, the contacts of which are located in the upper tier of PDZ (contacts 4,2,8 on the engine control sensor diagram) and are fixed on the plastic axis of the drive gear of the PDZ servo motor. During operation and contact friction, the resistor tracks of both potentiometers become thinner, their resistance changes (sometimes disappears due to rubbing). This leads to the fact that the resistance does not change proportionally to the rotation of the PDZ axis; the ECU does not correctly determine the position of the PDZ. In this case, it is necessary to change the PDZ board or the entire PDZ assembly, which costs from 8,000 to 15 thousand rubles + diagnostics and adaptation of 2,500 rubles.
But you can save money and ride another 90,000 thousand kilometers.
Due to the fact that the angle of rotation of the PDZ gear from the servomotor is not large, you can turn a pair of spring-loaded contacts of the plastic axis of the PDZ servomotor drive gear at a small angle counterclockwise so that the contacts move along another sector of the unworn resistor track. The resistance will change a little, but it will change smoothly proportionally depending on the rotation of the gear rotated by the servo motor, the ECU will begin to correctly determine the position of the remote control, corrected by the remote sensing drive.
Everything needs to be collected in starting position, connect all sensors and connectors, turn on the ignition, press the gas pedal all the way and release, wait 15 seconds and turn off the ignition. Repeat the same thing, but after 15 seconds, start the starter, pressing the gas a little. The PDZ must adapt its new position and the ECU will accept a new resistance value corresponding to the PDZ position at idle.
After adapting the PDZ parameters, the effect of the engine speed fluctuating disappeared, sometimes it stalls at idle, but this is easily corrected by the ECU, the main thing is that the effect of spontaneous changes in engine speed has disappeared. We connect the scanner, press the ECU learning reset button and that’s it, our machine is like new. On the Chevrolet Lacetti, learning can only be reset from the scanner. Disconnecting from the battery, as it turned out, only resets some errors.
In the future, if you want to do anything with the ECU system or remove any sensors, be sure to disconnect the negative from the battery.