The BMW 530i started the car, and the idle speed fluctuated. Why?

1, too much carbon deposit in the throttle.

2. Leakage of intake manifold or various valves. This fault directly affects the quality and combustion effect of fuel mixture. Parts that may leak air, such as intake manifold, vacuum tube, activated carbon canister valve, exhaust gas recirculation (EGR) valve and positive crankcase ventilation (PCV) valve, need to be overhauled one by one.

3. Valve timing failure. Valve timing dislocation, incorrect installation of timing belt, excessive carbon deposition in intake and exhaust valves, valve spring fracture, etc. The idle speed will be unstable due to the different air intake of each cylinder.

4. The three-way catalytic converter is blocked. The blockage of three-way catalytic converter not only leads to unstable idle speed, but also leads to insufficient power.

5. The fuel injector is faulty. For example, the nozzle atomization is not good, the nozzle is blocked, and the nozzle needs cleaning.

6. Fuel pressure is too low. Mainly check whether the fuel filter, fuel pump and other components are blocked and whether the oil pipe is deformed.

7. The engine stalled.

8. The ignition advance angle is too large or too small. Most of them are the problems of various signal sensors, such as intake air flow sensor, Hall sensor, knock sensor, coolant temperature sensor and so on. , need to be combined with the detector for analysis.

9. The cold car starts. When the cold car is started, the engine has large fuel injection and high idle speed, especially if it is not started for a long time or in a cold environment, the engine temperature will return to normal after it comes up.