What is the reason why the body still shakes after replacing the spark plug?

Engine jitter may be caused by weak spark of spark plug, so it will cause jitter. There are several reasons: 1, the performance of the spark plug is degraded, or the replacement spark plug has the wrong specification. After the spark plug reaches its service life, carbon deposition and ablation will appear on the electrode. Carbon deposition on the electrode will cause the difference of ignition energy, while electrode ablation will increase the gap. When the gap becomes larger, it will become difficult to generate an arc. At this time, it is easy to cause jitter due to lack of fire. This jitter is not continuous, but unintentional jitter. If there is a serious lack of fire, then there is a direct lack of cylinder and the vibration continues. 2, the ignition coil aging, performance degradation. The ignition coil provides the spark plug with the energy to generate an arc. If the ignition coil is aging, it can't provide the energy needed for ignition, especially for some old cars. Cold cars don't sway, hot cars sway. This is because the internal resistance of the ignition coil changes due to high temperature, which affects the ignition energy. 3. The nozzle is dirty or stuck, resulting in poor fuel injection. Poor atomization of fuel injection will lead to the decrease of intake air concentration and speed. At this time, the driving computer will increase the fuel injection time to correct it. However, when the fuel injector is out of order, it is difficult for the correction value of the driving computer to achieve the purpose of accurate control, which will cause serious idle jitter. At this time, it is necessary to clean the injector, preferably together with the intake pipe, because the injector is installed in the intake manifold, and the blockage of the injector is mostly caused by excessive carbon deposition in the intake pipe. 4 air intake: air intake refers to carbon deposition at the air intake, carbon deposition at the throttle and air filtration. Ignition: Check the spark plug, ignition coil and ignition system. Fuel supply: check the fuel pressure, fuel pump, oil products, carbon deposit in fuel nozzle, etc. Exhaust: check whether the three-way catalyst is blocked. Engine fixing: Whether the fixing bracket is damaged or aged and loses its buffering function. If there are no problems above, it is recommended to consider the internal problems of the engine, and the deformation of the piston connecting rod and crankshaft will also cause abnormal engine jitter.