A Volkswagen ten miles 1.8T FSI car with a mileage of about 18 thousand km in 2007. User response: the car is shaking at idle speed and is unable to drive normally. After taking the car, first use VAS 5052A to check the engine system, and find that the system stores multiple fault codes: 00768 () - random / multi cylinder detects no fire; 00772 () ----4 cylinder does not detect fire; 00771 () ----3 cylinder does not detect fire; 00770 () ----2 cylinder does not detect fire; 00769 () ----1 cylinder No fire was detected. The trouble code can be seen that the engine is a typical multi cylinder misfire fault. Ask the customer to know that when the vehicle is doing its first maintenance, it does not refer to the opinion of the maintenance station to add G17 fuel additive. First, it was suspected that the engine jitter was caused by the plugging of the fuel injector, so the fuel additive was added to the fault vehicle and the injector was removed and cleaned by ultrasonic. After loading, the failure is still. Strangely, a new malfunction appeared during the road test: the engine idling reached 1100 r/min, which was higher than the normal value. Through inspection, it is found that there is more than one fault code in the engine system: 01287 (), meaning that the idle speed of the control system is higher than the expected value. In view of these faults, the car was replaced by spark plugs, injectors and ignition coils, but failed to find out the cause of the failure. Then check the fuel pressure and cylinder pressure in normal range. There was no problem with the ignition and fuel delivery system, so the focus was shifted to the intake system. Using the fault diagnosis instrument to read the 01-08-002 area of the data flow, it is found that the intake volume is 1.4 g/s, while the normal idling value should be from 2.0g/s to 4.0g/s, and the measured data are obviously lower than the normal range. It is therefore suspected that the failure of the vehicle's fire and idling is caused by the damage of the air flow sensor. The damaged air flow sensor conveys the wrong intake data to the engine control unit, so that the engine control unit can not accurately control the parameters of the fuel injection and ignition time, which can lead to the abnormal or even fire phenomenon of the combustion. Change the air flow sensor and troubleshooting.