The idling speed of the Chevrolet Lacetti is floating. Ignition problems

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 PDZ potentiometer, the contacts of which are located in the upper tier of PDZ (contacts 4,2,8 on the circuit of engine control sensors) and are fixed on the plastic axis of the PDZ servo motor drive gear. During operation and friction of the contacts, the resistor tracks of both potentiometers become thinner, their resistance changes (sometimes disappears as a result of rubbing them). This leads to the fact that the resistance does not change in proportion 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 assembly, which is from 8000 to 15 thousand rubles + diagnostics and adaptation of 2500 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 servo motor is not large, you can turn a pair of spring-loaded contacts of the plastic axis of the PDZ servo motor drive gear by a small angle counterclockwise so that the contacts move along another sector of the not wiped resistor track. The resistance will change slightly, but it will smoothly proportionally change depending on the rotation of the gear rotated by the servo-motor, the ECU will begin to correctly determine the position of the DZ, which is being corrected by the DZ drive.
It is necessary to assemble everything to its original position, dock all the sensors and connectors, turn on the ignition, press the gas pedal all the way and release it, wait 15 seconds and turn off the ignition. Repeat the same thing but after 15 seconds start the starter, slightly pressing the gas. PDZ must adapt its new position and the ECU will accept a new resistance value corresponding to the DZ position at XX.
After adapting the PDZ parameters, the effect of the engine speed roaming has passed, sometimes it stalls at idle, but this is easily corrected by the ECU, the main thing is that the effect of spontaneous change in engine speed has disappeared. We connect the scanner, press the button to reset the ECU learning and that's it, our machine is like new. On the Chevrolet Lacetti, reset learning only from the scanner. Disconnecting from the battery, as it turned out, only clears some errors.
For the future, if you want to do something with the ECU system or remove any sensors, be sure to disconnect the minus from the battery.

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

Possible malfunctions

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

Consider the main causes of floating engine speed:

• Malfunction in the fuel system.
• Ignition problems.
• ECU errors.
• Poor quality fuel.

All these reasons are responsible for the appearance of such an effect. The most common cause is the appearance of injection problems.

Repair methods

Before proceeding to fix the problem, it is worth noting that floating rpm is just the beginning, since untimely troubleshooting 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 revolutions appear in the case of an uneven supply of fuel to the combustion chambers, or a constant change in the amount of the fuel mixture. This is primarily due to the injectors, which can be dirty. At the same time, it may not be felt when driving, but at idle, the tachometer will immediately show it. Therefore, it is necessary to dismantle and check the injectors on a special stand.

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

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

Ignition problems

Idling problems can occur due to improper operation of the ignition system. Namely, it could 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 the wires that go from it ring for operability.

ECU errors

Often, a car malfunction is associated with errors in the electronic control unit, as well as with 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 their operating system, but this does not always help.

As practice shows, a malfunction of an ECU can be a problem for the performance of many systems. Therefore, if it was not possible to eliminate the malfunction by the previous methods, it is necessary to replace the control unit.

Low-quality fuel

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

Output

Floating idle speed of the Chevrolet Lacetti engine can cause 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 revs, car owners had to use an electronic control unit.

Letters began to come to my mail with the problem of high revs when starting the engine. Immediately, the arrow rises by about 3,000 and after a few seconds falls to its normal position. We will argue logically. Why do engine speed depend on us? The revs are directly related to the opening angle of the throttle valve. The greater the angle it is open, the higher the engine speed. Whoever has a BC, the easier it is, they can just look at the readings of the IAC and determine whether this is the case. Those who do not have a bookmaker will need the help of a friend. You need to put him on 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 throttle cable is attached). You can watch the video on the page:. This lever is fully connected to the IAC - idle speed regulator. Ask a friend to turn on the ignition. The lever should tilt to the left, opening the throttle 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 by 3,000 rpm, and when the speed drops, the lever together with the damper will close, then it’s the IAC. Turnovers correspond to the position of the remote control.

Let's look at another option. Let's say our IAC is working properly. Because of what the turnover can rise? I often go to forums to see what new sores are popping up on our cars. And there is a wrong opinion. The question is: "Why small turnovers?" And in the answers they write that you need to look at all the hoses, if there are any cracks and if there is air leakage. They write correctly, but only for cars with a 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 it. It turns out that more air passes into the engine, and the mixture becomes leaner, which leads to a decrease in rpm.
... ... With us, the opposite is true. There is a DBP, and it determines the absolute pressure in the intake manifold. If there is an air leak, then he will catch it. It turns out that the damper passes its portion of air, and the suction adds its own. DBP takes into account everything, and the revolutions increase. And in any case, the injectors inject as much gasoline as needed for the engine to function properly. 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 DZ - the throttle valve, and everything will be settled. The next time you start it, everything should be repeated. Now let's think about where the excess air can come from, other than bursting hoses. Three systems come to mind, although even 4.

If the piston is jammed or the spring burst in the pcv valve - crankcase gas removal, 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 properly, then 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 faulty, then gasoline vapors will also go through the pipe 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, looks like 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. In this mechanism itself there is a membrane - a diaphragm, and if it is torn, then air will flow through these tubes into the manifold until the engine exceeds 4000 rpm. And then just switch to a short collector and close this circle. Tomorrow we have Monday, I will 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 will behave. Then we will definitely find out whether our theoretical conclusions and logical chain are correct. OK, see you tomorrow. I think by the evening by 10 o'clock I will post the video both on the blog and on YouTube.
... ... Well, everything is ready.