The mileage is about 90 thousand km, and the Volkswagen Phaeton is imported in 2010 with the 3.0L TFSI engine. User response: there is a problem of irregular flameout and idle jitter. Inspection and analysis: the maintenance personnel failed to find fault. Check engine and transmission control unit, trouble free code. So the engine and transmission control unit control procedures refreshed after the delivery. A few days later the user reflected the failure again. When the vehicle comes to the factory again, the maintenance personnel suggest that the user observe the car in the factory. The first day of the second day started very smoothly, and the failure did not appear. After a period of fire, the restart failure has not yet appeared. The engine control unit is detected by VAS6150, and no fault code is stored. In this case, a long time trial run is needed to wait for the failure to occur. After a day's trial run, some rules of the malfunction were finally grasped. After a long period of high-speed vehicle driving, the engine is restarted after 10 min, and in this case, sometimes the engine will have severe jitter when it is idle, and the engine will still be flameout to a certain extent. After the fault occurs, seize the time to detect the engine control unit, without any fault code storage. Suspicion is that some parts are abnormal after being heated. So it decided to try the part replacement. However, after the replacement of ignition coils, spark plugs, low pressure oil pumps, high pressure oil pumps, fuel filters, injectors, air filters, turbochargers, activated carbon tanks, coolant temperature sensors, air flow meters and crankshaft position sensors, and after cleaning the intake, throttle and crankcase ventilation pipes, the problem remains. It has not been solved. It seems that the reason behind the fault is still a bit of mental ability. In the next few days, the maintenance personnel fully check all the parts related to the engine operation, but still fail to find out the real cause of the failure. At this point, we can talk about the end of the world. After observing a fault phenomenon after a high speed running, it is incidentally found that the intake temperature data in the data stream of the engine are abnormal. The intake temperature at this time reached 107 degrees centigrade, and the ambient temperature was only 23 C at that time. Such a large temperature difference was seldom seen before. According to the characteristics of the air, its density will decrease with the increase of temperature. At extremely high temperatures, the air density will be very low. As a result, the actual air quality of the actual inhalation engine can not reach the requirements of the normal operation of the engine, that is to say, the actual output torque of the engine is lower than the expected value. It seems that the solution to the problem has finally come to a glimmer of hope. When the upper cover of the air cleaner is opened, the intake temperature drops rapidly. It is evident that the high temperature air flow is coming from inside the engine rather than the engine compartment. Where does the air flow from such a high temperature come from? Careful observation shows that a plastic pipe on the top of the air cleaner has been roasted and deformed. Following this tube, it is found that it is the two intake pipe of the air pump. The two air system belongs to the environmental protection component. When the engine starts, due to the use of a strong mixture, the combustion of some of the fuel is not completely combustion generated pollutants - hydrocarbons. So in a period of time after the start of the engine, the two air pump will send a certain amount of fresh air into the exhaust pipe. The purpose is to use the higher exhaust temperature to keep the fuel that is not completely burning, in order to reduce the pollution of the atmosphere and improve the temperature of the catalytic converter. The two air system works 100s after starting the engine cold car. After the hot car starts, it works 10s or does not work at all. The two air system is composed of an air pump, a combined valve, an air pipe, a vacuum source and a solenoid valve of the control combination valve. The combination valve is installed at the rear part of the 2 row cylinder and communicates with the exhaust passage on the cylinder head. The air pump and solenoid valve are controlled by the engine control unit. When the system works, the air pump operates, and the solenoid valve opens the vacuum source. The combined valve is opened under vacuum. Fresh air enters the exhaust passage through air filters, air pumps, pipes and combined valves. When the system is not working, the combination valve is closed, and the air circulation of the air passage is cut off. After understanding the principles of the two air system, the cause of the failure is broken. It is because the combination valve is stuck and sometimes closed, resulting in the airflow of the exhaust passage directly entering the air cleaner from the gap of the valve. After the engine inhaled the hot air, the idle speed of the engine was not adjusted enough to cause the engine to idle until it was extinguished. Troubleshooting: replace the combination valve, troubleshooting.