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The mileage is about 90 thousand km, the Audi Q5 sport utility vehicle with CAD engine and OBK automatic transmission in 2011. Users reflect: the car idling jitter, engine fault lights. Inspection analysis: the maintenance personnel use VAS5052A to detect the engine control unit, found fault code 00768 - multi cylinder detection of fire; 00769-1 cylinder measured fire; 00770-2 cylinder measured fire; 00771-3 cylinder measured fire; 00772-4 cylinder measured fire. Through the fire flow data group 01-08-015, the number of misfire in the 1-4 cylinder is read, which is 1 cylinder 20, 2 cylinder 43, 3 cylinder 36, 4 cylinder 20. The number of normal vehicles should be 0. Low pressure oil pressure was detected by special tool VAG1318, 350 kPa, normal. Read data block 01-08-106, high pressure oil pressure is 4 M Pa, also normal. Remove the retaining plate on the engine and find the squeak of the air flow near the crankcase ventilation valve (Fig. 1). To determine the correlation between exhaust valve failures and turn on the oil filler cap, it is obvious that the crankcase vacuum is very high. Block the crankcase ventilation to the intake manifold, the engine runs smoothly, and the fault phenomenon vanishes. The crankcase ventilation valve is used to regulate the exhaust gas of the crankcase that enters the engine. When the engine is working, it keeps the crankcase a certain degree of vacuum and ensures a good crankcase ventilation. It consists of 2 chambers, and the two are separated by diaphragms. One chamber passes through the atmosphere, and the other chamber passes through the intake manifold and the oil gas separator. When the vacuum in the intake manifold increases, the vacuum in the crankcase also increases. To prevent this from happening, the ventilation valve is used to regulate the size of the gas passage, thus controlling the gas flow through the valve in the proper range. As the diaphragm of the valve is damaged, the air pressure in the 2 chambers is equal, and the springs in the valve are in free state, which makes the gas path always in the maximum opening state. The engine inhaled too much crankcase exhaust, causing the engine to shake. Troubleshooting: replace crankcase ventilation valve assembly, troubleshooting.