When the engine is working, the driver manipulates the opening of the throttle valve through the accelerator pedal, so as to change the intake air volume and control the operation of the engine. After the air entering the engine is filtered by the air filter to remove dust and other impurities, it flows through the air flow meter, enters the power chamber along the throttle valve passage, and is distributed to each cylinder through the intake manifold; The air bypasses the throttle valve and enters the cylinder through the additional air valve or idle speed control valve.