Roewe 550 idling is unstable, and the tachometer is up and down.

Idle speed instability may have the following reasons:

1, engine carbon deposit is serious.

When there is too much carbon deposit in the engine, the gasoline sprayed by the fuel injection head will be absorbed by the carbon deposit during the cold start, which leads to the lean mixture during the cold start and makes it difficult to start. In this case, only when the gasoline adsorbed by carbon deposits is saturated, it is easy to run into the car. After running into the car, the gasoline adsorbed on carbon deposits will be sucked into the cylinder by the vacuum suction of the engine for combustion, which will thicken the mixture and dilute the combustible mixture of the engine, resulting in idling jitter after cold start.

2. There is too much scale on the throttle and air intake.

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.

3. Individual spark plug failures cause the spark plug to be too weak.

Spark plugs will also deposit carbon, which can be cleaned to restore the activity of spark plugs, but some spark plugs will have poor performance when their service life is approaching. The spark plugs on individual cylinders are weak, which will affect the performance of the car. Spark plug failure will lead to "fire" symptoms of the car, but spark plug failure of individual cylinders will lead to unstable idle speed symptoms.

4. Fuel pressure failure

If the oil pressure is too low, the fuel sprayed by the injector is in poor atomization state or the fuel sprayed is linear. In severe cases, only oil droplets are sprayed, and the fuel injection quantity is reduced, making the mixture too thin; When the oil pressure is too high, the actual fuel injection increases, making the mixture too rich.

5, all kinds of parts failure

Leakage of intake manifold or various valves, fuel pressure failure, low oil pressure, ignition system failure, etc. , it will also cause the engine idling instability.