Fault phenomenon: when TOYOTA corolla motor changes its speed, the selector rod will enter all d gear, and the engine speed will drop sharply. Sometimes the engine will still stall. I started thinking that the transmission oil was not good, so I changed the transmission oil. However, the replacement of oil has no effect, the fault symptoms are exactly the same as before. Troubleshooting inspection process must first be clear whether the engine is running off because of the transmission or the engine itself. In the D gear, the 2 gear and the L gear, the engine is not running well, and the R gear is not faulty. In this way, it can be denied that the engine operation is not adjusted because of the automatic transmission problem, because the engine speed of the engine caused by the automatic transmission problem drops sharply or even extinguish. The locking clutch of the torque converter must be concluded. If the lock clutch is concluded, there should be no way forward or backward. Failure phenomenon, thus the problem in the engine. Open the hood of the engine room and observe the appearance of the shift selector in the D gear and the R gear at idle speed. When the speed selector is placed in the D gear, the engine vibrate after a change of speed, and it stalls for a few seconds. Start the engine again. When the gear changes, step on the accelerator pedal slightly, and the engine does not stop. The engine was flameout as a result of vibration. Stepping on the accelerator pedal does not cause flameout. This shows that there is no wiring, breakage and so on. After repeated flameout several times, the cause of the stall was also found, on the air duct. This engine uses air measuring plate air flow meter, type L Ye Te Rangnick (L-jetronic) electronic control fuel injection system. The air conduit between the air flow meter and the throttle chamber is corrugated. It can be expanded with the change of the intake of the engine. After years of use, many repeated expansion and repeated expansion will produce cracks. Because the variable selection rod is changed into the forward gear, the corrugated air duct extends forward, the crack expands, the air enters the cylinder without the air flow meter, and the air fuel ratio of the mixture is too thin to extinguish the engine. The reason that the acceleration pedal does not gasp is that the air flow into the cylinder is more than the air flow meter, and the air volume that enters the cylinder through the tube crack is relatively reduced. The gear selector is placed in the R gear, the bellows tend to shrink, and the cracks are blocked.