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Q: a MITSUBISHI V73 sport utility vehicle is equipped with 5 speed automatic transmission, which uses an electronic throttle. The user reflects that the idle speed of the vehicle engine can only be reduced to 800 r/min after a few minutes before the start of the hot car cooling car at 1500 r/min. If the gearshift is operated at this time, the engine speed will fall about 400 r/min, sometimes the engine will even be flameout, and the transmission is also accompanied by a sense of impact. The vehicle has no problems after starting and running. The connection fault diagnosis instrument detects the engine control system and the automatic transmission control system, and the diagnostic instrument does not show that there are fault codes stored in the two systems. Please help analyze the reason. Answer: through your description of the car failure phenomenon, the engine speed fall too much is abnormal when the original power gear is hung, and in normal circumstances, when the automatic transmission gear is hung, the engine speed should have a decrease of about 100 to 200r/min, and it will also quickly rise to the normal engine idle speed. According to our experience, this kind of fault may be an engine problem or an automatic transmission problem. For engine problems, possible causes of failure include dirty throttle body and insufficient intake capacity. For the problem of automatic transmission, this phenomenon is usually produced when the locking clutch of the torque converter is in the joint or semi joint state, that is, the automatic clutch function of the torque converter is invalid (soft connection function). In addition, this phenomenon may occur when the oil pressure of the automatic transmission system is too high. During the maintenance process, the relevant data of the engine control system should be looked at first, including the throttle opening signal, the coolant signal and the engine intake signal. The appropriate cleaning, adjustment, repair, replacement or matching should be required when necessary. (note that the engine hot car should not be high idle when starting the engine, so the engine should not have high idle speed. Attention should also be paid to the signal of coolant temperature sensor. In addition, in the transmission, according to our experience, the automatic transmission control unit will never send out the joint instruction of the torque converter lock clutch when it is in place (it can be seen from the data flow). If the function of its automatic clutch fails, the problem is not necessarily on the torque converter. At this time, the quality of the oil liquid of the automatic transmission should be determined first, because when the oil quality of the automatic transmission is worse, the fluid of the original transmission is poor at low temperature. If there are impurities or particles in the liquid, it will affect the normal action of the valve, and there may be sticky or stagnation. The appearance of the failure phenomenon. In addition, it can also connect the oil pressure gauge to the main oil pressure test of the automatic transmission, and pay attention to observe whether the oil pressure of the system pipeline is too high when the fault occurs. Therefore, it may be possible to carry out the maintenance of the transmission (including the clean hydraulic system), perhaps the problem can be solved. Of course, it is necessary to carry out the necessary cleaning of the hydraulic control valve when necessary. This operation requires professional maintenance personnel to operate. But don't make a mountain out of a molehill. When your mind is clear, you can solve big problems through simple processing.