When the engine is idling, the throttle opening is smaller than when the engine is not working, right? Why?

The technical basis of engine idle speed control is to change the air intake at idle speed, so as to obtain a suitable idle speed. There are two ways to change the air intake, one is the bypass channel; The second type is the main airway type. Bypass type, as long as the engine is at idle speed, no matter whether the engine is running, fast idling or forced idling, the throttle valve is always in the closed position, and the intake air volume is adjusted by opening the bypass. In the main port adjustment mode, the adjustment of idle speed is realized by the change of throttle opening. When the engine is turned off, the throttle valve is properly opened at an angle so as to start the car again.