A Volkswagen Passat B5, with a mileage of about 180 thousand km, equipped with a 1.8L double camshaft engine and a manual transmission. Owners reflect: the engine jitter is serious, and the vibration inside the vehicle is obvious. Fault diagnosis: first, the engine electronic control system is detected by the detector, and the fault code P0332 deflagration sensor circuit fault is displayed. After the fault code is removed, the fault data is not seen in the trial run, and the engine data flow is checked. The data are displayed within normal limits, indicating that the electrical part is working normally. Measure cylinder pressure, check the spark plug is not abnormal, check the vacuum pipeline again. No air leakage is found. According to the driver, two weeks ago, the car was overhauled because of the valve top bend. It was preliminarily suspected that the double cam chain was not aligned at the time of assembly, and the phase of the matching gas was not jitter. Open the valve chamber cover gasket, check the timing chain mark carefully, and find that the 17 chain sticks should be 16 chain sticks correctly. After the ignition is corrected, the engine still jitter, indicating that this is not the main cause of jitter. Further inspection revealed that the rubber fracture of the engine support was replaced by the replacement of the engine support cushion, but the jitter effect was somewhat weakened, but it was not completely eliminated. After eliminating electrical, leakage, gas phase, fixed support and other reasons, the fault range is still determined in the mechanical problem. It may be thought that the dynamic balance of the rotating parts does not cause the jitter. Unbalanced parts such as crankshafts and flywheels cause jitter. So first lift the engine, look at the flywheel, found that the first, second mass relative rotation is too large, is the torsional bearing damage caused by the big flywheel and the small flywheel can not be concentric rotation, causing jitter. Replacement of double flywheels, no jitter after launch, troubleshooting. Maintenance summary: there are many causes of engine jitter, which are roughly divided into electrical components and circuit damage, vacuum pipeline leakage vacuum, gas phase misalignment, unbalance of rotating components, related support damage and so on.