What is the reason for the unstable idle speed of BMW engine?

Jitter is a common problem of all kinds of cars at idle speed, especially after the cold car starts, it is easier to idle unsteadily or shake the body. The most fundamental reason of jitter phenomenon is poor combustion in cylinder. If the combustion is not good, the power provided by the car is not enough, and the car will shake. ?

Engine idling instability will be caused by mechanical failures of intake system, fuel system, ignition system and engine. Therefore, it is a wide-ranging and difficult job to diagnose the cause of engine idling instability, and it is not appropriate to replace parts easily. There are many reasons for the unstable idle speed, and correct judgment should be made according to the test results, theoretical analysis and maintenance experience, so the diagnosis work is regular.

Idle instability may be caused by the following points: 1, too much dirt on the spark plug surface after long-term maintenance, so replace it after 30,000 kilometers. 2. The fuel injector and throttle valve are not cleaned and maintained. 3. There is too much sludge in the engine, or too much carbon deposit when driving at low speed for a long time, and the oil and machine filter are not replaced in time. 4. The poor oil circuit may also cause unstable idle speed, and these problems will also occur when the famous brand gas station refuels for a long time or changes the gasoline filter irregularly. 5. It is also possible that there is something wrong with the driving computer, which leads to the wrong command.

Troubleshooting methods generally include: cleaning the throttle and air intake, cleaning and checking the fuel injector, replacing electrical components, checking the fault point of the wiring harness, cleaning the grounding point, and repairing the mechanical structure of the engine.