A Ford Carnival car with a mileage of about 72 thousand km. When the vehicle is running at high speed, it loosely accelerates the pedal engine to stall. During driving, when the speed is higher than 80 ~ 90km/h, the neutral skating is often flameout, and it is not easy to stall at low speed. According to customers, when the fault just appeared, the oxygen sensor was removed at other repair stations, and no problems were found. Fault diagnosis: WDS is detected by diagnostic instrument, and no fault code is displayed. Reading the data is basically normal, but when the engine is idle, only the throttle opening value is at the upper limit of the standard value. Now it is doubtful that the throttle is too dirty, when the vehicle is suddenly loosed and accelerates the pedal or the idle speed of the brake pedal, the intake of the throttle is too small to make the engine stall. Cleaning throttle, re setting, commissioning, failure has not ruled out. There is still no fault code for re testing, but valve opening is normal at idle speed. After checking the intake manifold, it is found that the connection of the air cleaner outlet is loose and leaking, and is tightened again without any other abnormalities. Test the car, troubleshooting.