The idle speed is unstable and the exhaust pipe suddenly makes noise. What is the reason?

Common fault points of unstable idle speed of automobiles are as follows:

1. Leakage of intake manifold or various valves.

If the intake of the engine is incorrect, the mixture will be too rich or too thin, which will make the engine burn abnormally. Will lead to engine idling jitter.

When the position of air leakage affects the vacuum degree of the engine, the engine will shake violently, which has a great influence on the idle speed of the cold car.

Common reasons are: air leakage caused by aging of intake manifold gasket, damaged intake manifold or worn holes of other parts, vacuum tube plug falling off, EGR valve damaged and not closed properly, etc.

2. There is too much dirt on the throttle and air inlet.

There is too much carbon and dirt in the throttle and the surrounding air intake, and the cross-sectional area of the air passage changes, which makes the control unit unable to accurately control the idle intake, resulting in the mixture being too rich or too thin, which makes the combustion abnormal.

The common reasons are: carbon deposition on the throttle, and oil pollution and carbon deposition on the air intake around the throttle.

3. Idle air actuator failure

Idle air actuator failure leads to inaccurate idle air control.

The common reasons are: the throttle motor is damaged or stuck, and the throttle valve plate is stuck with carbon deposition.

4. Incorrect air intake

The control unit receives the wrong air flow sensor signal and sends out the wrong command, which leads to inaccurate air intake at idle speed of the engine and abnormal combustion of the engine due to abnormal mixture concentration, which is the indirect cause of unstable idle speed.

Common causes are: air flowmeter or its line failure; Intake pressure sensor or its line fault; Poor contact of engine control unit harness or failure of engine control side itself.

It is recommended to check the above components when the vehicle is idling unsteadily.