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A mileage car with a mileage of about 60 thousand km and a 2.5L engine equipped with 2006 Ford Changan Mondeo cars. User reflection: the engine is normal after the car is started, and the idle speed is obvious after the hot car. The speed fluctuates between 750 and 850r/min, and the emergency brake has the phenomenon of flameout. After receiving the car: the idle speed control valve, throttle, intake port and injector are cleaned. After completing the commissioning, the trouble remains. Measure the pressure of fuel, normal. Replacement of spark plugs, high voltage lines and ignition coils continues. There are two fault codes P1151, P1131, which are related to the fault of oxygen sensors. The oxygen sensor is replaced, and the fault is not excluded. In view of the data flow, the system can enter the closed loop state, but the signal voltage of the oxygen sensor is always on the low side and remains unchanged at 0. 0V, and the long-term and short-term fuel correction coefficient is in the trend of greater than 0. The above data shows too much oxygen in the exhaust gas, but it does not mean that the mixture itself must be dilute, because such problems may occur because of poor ignition, air leakage or low compression ratio. Check the appearance of the engine and find that the vacuum tube below the throttle valve is broken. Replacement of the vacuum tube, trial run, trouble shooting. In the cold vehicle condition, the engine provides a strong mixture, although there is air leakage, but it is not obvious. When the hot truck stops working, the gas leakage will obviously affect the concentration of the mixture, and the cylinder will not work well.