The mileage is about 90 thousand km, the Audi Q5 sport utility vehicle with CAD engine and 0BK automatic transmission in 2011. Users reflect: the car idling jitter, engine fault lights. Inspection and analysis: the maintenance personnel ran the test and found that the engine of the vehicle was obviously lack of cylinder. Using VAS5052A to detect engine control unit, it is found that there are 2 cylinder fire failure tips. Reading data found that 2 cylinders were more frequent during idling. When the idle speed is raised, the number of fire loss is reduced. Check the ignition coil and spark plug of the 2 cylinder, do not find any abnormalities, replace the spark plug and ignition coil with the 1 cylinder, and the trouble can not be ruled out. There are more carbon deposits when the inlet is removed. After cleaning the intake port and cleaning the fuel injector, the test found that the fault remained. For further inspection, the cylinder pressure of the 2 cylinder is normal, but the 2 cylinder fire also indicates the possibility of mechanical failure. In this case, only the cylinder head is removed, and the intake valve, exhaust valve, valve spring and rocker assembly are checked. It was found that the radial clearance of the needle bearing of one exhaust valve rocker arm is larger. Damage and deformation of the valve rocker arm (Fig. 1), resulting in a reduction in valve lift, which affects the valve mass of the valve. Troubleshooting: replace exhaust valve rocker, test run to confirm troubleshooting.