The Honda Guangzhou 1. 5L car with a mileage of about 135 thousand km in 2008. Owners reflect: after the repair of an accident, the vehicle appeared regular jitter in idle speed, and there was no fault before. Fault diagnosis: 1) after the vehicle is tested, when the engine is idle, the steering wheel is held in the driver's cab, and the jitter of the engine is obviously felt. When stepping on the accelerator pedal, when the engine speed reaches 1500r/min, the jitter failure will disappear, and there will be no acceleration failure when driving. 2) keep the engine idle and read the engine trouble code with HDS without any indication. 3) the car owner reflected that the car had been overhauled once, checked in other maintenance plants, and replaced the spark plug, the ignition coil, the injector, and the jitter was more severe after the repair. 4) remove the ignition coil. When checking, it is found that the ignition coil is not the original accessories. After the replacement of the 4 ignition coils, the jitter is reduced, but the fault still exists. 5) at last, the spark plug was removed, and the spark plug was found as an ordinary spark plug. After the replacement of the iridium spark plug in the original Honda factory, the starting engine was tested. The engine idle speed was normal and the failure was eliminated.