The idle speed of rc390 is unstable.

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 absorbed by carbon deposits is saturated can it easily enter the car. After entering the car, the gasoline adsorbed on the carbon deposit will be sucked into the cylinder by the vacuum suction of the engine for combustion, which will enrich the mixture and dilute and concentrate the combustible mixture of the engine.

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

3. The spark plugs caused by individual spark plug failures are too weak, and the spark plugs will also accumulate carbon, which can be cleaned to restore the spark plug activity, but the service life of some spark plugs is approaching, and the performance will also decline. 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. The fuel pressure is faulty, the oil pressure is too low, the fuel sprayed by the injector is in poor atomization state or the sprayed fuel is linear, and in severe cases, only oil droplets are sprayed, so that the fuel injection quantity is reduced to make the mixture too thin; When the oil pressure is too high, the actual fuel injection increases, making the mixture too rich;

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