A mileage of about 90 thousand km, a Audi Q5 sport utility vehicle equipped with CAD engine in 2010. User reflection: the car idling jitter. After removing the valve chamber cover, take out the valve rocker inspection and find out that the clearance of the needle bearing of the 2 exhaust valve rocker arm (Fig. 1) of the 2 cylinder is very large. Compared with the rocker arm of other cylinders, it is confirmed that the gap is very different. It is obvious that the abnormal sound is produced during the operation of the needle bearing of the rocker arm, and this gap will affect the valve lift, and then affect the timing of the normal opening and closing of the 2 cylinder exhaust valve, resulting in the bad work of the cylinder. Inspection and analysis: maintenance personnel test run, found sitting in the car can feel jitter. The engine control unit was detected by the diagnostic instrument VAS5052, and a fault indication for 2 cylinders was found. Judging from the frequency of engine jitter, the fault should not be caused by the leakage of the intake system. Replace ignition coil and spark plug. There is no change in malfunction. The cylinder pressure is measured, and the cylinders are all above 1.2 MPa, normal. It is found that the jitter of the upper part of the engine is particularly obvious. Use the stethoscope to confirm that the location of the sound is in the valve chamber cover. It is judged that there is mechanical failure in the intake and exhaust mechanism of the engine cylinder head. Troubleshooting: replace valve rocker, test run to confirm troubleshooting.