What is the reason for the unstable idle speed of EFI vehicles?

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.