A TOYOTA Camry. Customer reflection: after finishing the maintenance, the car came back to find that the car was waiting for the red light, the body shook badly, and the acceleration was weak, and it always felt that the car could not run. After the vehicle enters the factory, the test car is confirmed, and it is found that there is an idle jitter, and the vehicle is obviously accelerated when the speed is accelerated and the power is insufficient. It is basically in line with the customer's description. Fault diagnosis: connect IT- II, enter the diagnostic system to check DTC, normal. It shows that the fault appears in the non self diagnosis system; it is found that the opening value of the throttle is 18% and the normal condition is about 15.6%, indicating that the throttle has a certain amount of carbon accumulation; the engine room visual inspection, the ventilation hose and the intake system are normal. After cleaning the throttle, check the throttle opening, normal. After starting, the failure is still. Clean oil road, check fuel pressure, normal. The cylinder is checked, and the cylinder injector connector is pulled out. When the engine is pulled to 4 cylinders, the engine speed has no obvious change, and the rest cylinders are normal. It shows that the 4 cylinder work is bad. Check the 4 cylinder injector circuit, injector are normal. Remove the spark plug and find that there is coke on the surface. When the spark plugging device is removed, the spark test is carried out. It is found that the spark is weak, and it is replaced by a normal ignition coil. The fault of the ignition coil of the 4 cylinder is explained. After careful examination, it is found that the leakage of the insulation layer causes leakage, resulting in insufficient secondary voltage affecting the normal combustion of the fuel. After the new igniter is replaced, the fault is ruled out. Maintenance summary: in this maintenance, because of no better analysis of the cause of the failure, the use of IT-II analysis data, a lot of curves, to the customer has brought a lot of inconvenience, and also give us a certain lesson. Regardless of any problems, we must have a coherent way to find out the cause of the failure, and use the tools and measuring tools reasonably. This way, we can avoid troubleshooting and remove the trouble as quickly and accurately as possible.