Idle

With the throttle valve closed (accelerator pedal released), a small amount of air passes through the passage bypassing the throttle valve. The quantity of this air is determined by the air flow meter or pressure sensor and is supplemented by the required amount of fuel to form the idle mixture. Incidentally, the idle mixture is richer than the normal mixture, which ensures that the engine runs smoothly without misfiring. The control unit determines when to enrich the idle mixture from the throttle position sensor. The amount of air passing through the bypass (and thus the idle speed range) is determined by the idle air control valve.