The Nanjing Fiat 1 3L car with a mileage of over 210 thousand km in 2004. Car owner reflects: the car accelerates bad. Fault diagnosis: after the repair technician receives the car, first start the engine test, the engine runs smoothly, the idle speed is about 800r/min (normal value is 750 ~ 850r/min), indicating that the engine idle speed is normal. Fast stepping down the accelerator pedal, the engine speed can not rise rapidly, but slowly improve, indicating that there is indeed a malfunction of acceleration. The Fiat special detector Examiner is connected to the engine electronic control system for detection. The results show first ignition coil fault, detonation sensor fault and oxygen sensor fault. After the fault code is cleared, the engine is restarted and the detector Examiner is used again. The instrument shows no fault code, but the phenomenon of bad acceleration still exists, without any improvement, which indicates that the above fault code is an accidental fault. Then the cylinder breaking and jumping test was carried out. The electric spark was very strong, indicating that the first point and second ignition coils were normal. When we try again, it is found that when the accelerator pedal is on the ground, the engine can speed up slowly, but the engine speed can reach 6000r/min in a little while, which indicates that the fuel mixture increase is slower. The initial judgment is that there is a problem in the air passage, and the fault is not closely related to the fuel supply system. Considering that the mileage of the vehicle has reached 200 thousand km, there is something wrong with the throttle. After asking the owner of the car that the car had not cleaned the throttle except for its normal maintenance, it decided to remove the throttle check. First disconnect the battery connection line, remove the engine computer (because the engine computer is above the throttle body), and break all the air pipes of the intake pipe, the connection plugs are pulled out, and finally the throttle is removed. After removing the throttle, it is found that the carbon deposition is very thick, which indicates that the malfunction of the car is directly related to throttle carbon deposition. After cleaning the throttle with brush and cleaning agent, start the car, start the engine, quickly step down the accelerator pedal, speed up the engine speed, and carry on the road test, the car accelerates forcefully, the speed is normal and the fault is completely eliminated. Maintenance summary: the cause of this failure is that there is no regular maintenance of the throttle body, resulting in a large amount of charcoal in the throttle body, the air channel becomes smaller, and then the amount of mixed gas increases slowly, and the engine accelerates. Under normal circumstances, every 15 thousand km driving vehicle, the throttle body should be thoroughly cleaned to ensure the normal operation of the engine.