A mileage of about 90 thousand km, equipped with BGC engine and 01V manual transmission, 2007 Volkswagen Passat controls 1.8T automatic car. User response: when the car sometimes stops at N stop, the engine speed suddenly rises to more than 3000 r/min. Inspection and analysis: maintenance personnel found that the car engine idle speed was stable, temporarily unable to detect abnormal phenomena. Using the VAS5052 fault diagnosis instrument to detect the engine control unit, only one fault code 16825---- is found, and the flow rate of the fuel tank ventilation system is abnormal. Delete the fault code after recording it. Then, the gasoline tank ventilation system is quickly tested (basically set 006-70), the screen display system is abnormal, the fault memory is inquired, and the fault code 16825 is reproduced. Out of the carbon tank solenoid valve N80 to the carbon tank of the pipeline, when the measured value of the 70 group 1 carbon tank solenoid valve control duty ratio of more than 40%, the hand can feel a larger vacuum suction. Check the N80 on the condition of power failure. It is found that the solenoid valve channel can still be blown through, indicating that the problem is here. Passat is more prone to this malfunction. Most of the fault points are on the N80 of the carbon tank solenoid valve. The reason is that activated carbon particles or other impurities in the activated carbon can easily be washed out of the air and stuck at the valve seat to make the N80 closed. In this way, it will cause different fault phenomena due to climatic conditions. When the car broke down in the winter, the gasoline steam in the tank was not much, and the oil tank was washed into the intake manifold when the N80 action was moved into the intake manifold, and the mixed gas was thinner. In the action of oxygen regulation, the idle speed increased. If the fault occurred in the summer, the gasoline vapor in the tank increased dramatically, and the fault table was now idle quenching and hard to start. Troubleshooting: replace the carbon tank solenoid valve, troubleshooting.