What is the reason for the unstable idle speed of Qingling engine?

It may be that there is too much scale on the throttle and air intake, too much carbon and dirt around the throttle and air intake, and the cross-sectional area of the air passage changes, which makes the control unit unable to accurately control the idle air intake, resulting in the mixture being too rich or too thin and abnormal combustion. It may be that the fuel injection quantity is inaccurate, and each sensor or line is faulty, which leads to the control unit giving wrong instructions, which makes the fuel injection quantity incorrect and causes the mixture to be too rich or too lean, which is the indirect reason for the unstable idle speed.