What is the reason why the idle speed suddenly rises and falls after cleaning the throttle?

Because the throttle opening has not been reset. The throttle is squeezed by long-term carbon deposition, and the throttle opening also becomes larger. If the throttle valve is not reset after cleaning, the throttle valve opening is still in the state before carbon deposition, and the phenomenon of unstable idle speed will occur when the intake air increases seriously. The following is the method to reset the throttle opening: 1. At present, most cars use electronic throttle, and a diagnostic instrument and a computer are needed to initialize the throttle in order to achieve normal idle speed. There are also some old models that use mechanical cable throttle, so these cars will gradually restore the throttle opening to the initial state in the future driving, and the idle speed will naturally stabilize. 2. For example, unplug the negative battery before cleaning the accelerator, or turn the key to the on position after cleaning, wait for a few minutes and then turn it to the ON position, and then start the car without stopping after stepping on the accelerator. This method is useful to some car owners, but it doesn't work. In fact, different models have different reset methods. The quickest way, of course, is to equip them with computers.