Why does the car shake before and after driving?

The main fault causes are the increase of carbon deposition in throttle, air intake and valve, and some gasoline is adsorbed when the car is cold. When the car is hot, the gasoline volatilizes, which will cause the mixture to be too rich when the engine is idling, which will lead to the unstable idling of the hot car.

So you should not only check the throttle and idle motor, but also check whether there is too much carbon and dirt at the air inlet. If there are too many carbon deposits and dirt, the cross-sectional area of the air passage will change, which will make the control unit unable to accurately control the idle intake air volume, resulting in too rich or too lean mixture, which will lead to abnormal combustion and engine jitter. At the same time, pay attention to check whether the carbon canister is faulty.