A car with a mileage of about 70 thousand km and a F02 730Li powered BMW 730Li car equipped with N54 engines. User reflection: the car idling jitter. Inspection and analysis: the maintenance personnel tried the car and found that the car had good performance except for idling jitter. Detect engine control unit and find fault code 274E - multiple cylinder misfire. After the fault code is cleared, the engine is idle, and the same failure code appears again as the jitter continues. After the fault code is removed, the idle speed is increased to 2000 r/min. At this time, the engine runs smoothly, and the fault code does not appear again. As the fault occurs only in the idle phase of engine operation, the cause of the failure is concentrated on the intake system. Considering that the engine is controlled by the intake valve, the uneven distribution of the inlet valve carbon in the cylinders often leads to the phenomenon of fire in individual cylinders. It can be judged that the fault of the vehicle is caused by coke deposition. Troubleshooting: cleaning the intake valve carbon deposit, commissioning confirmation troubleshooting.