Auxiliary Air Valve (Idle Speed): Description and Operation

Fig. 15 Auxiliary Air Valve:

The auxiliary air valve, Fig. 15, operates in conjunction with the warm up regulator to compensate for losses due to friction and condensation in the intake manifold and combustion chamber during cold starting, so a constant idle speed can be maintained. The valve is located in a bypass passage around the throttle plate. The air flowing through the auxiliary air valve has been metered by the air flow meter, so no unmetered air is introduced into the air system. The valve is actuated by a bi-metallic strip that opens the valve when the engine is cold. When the engine is started, current flows through a coil, heating the strip and gradually closing the valve. When a warm engine is started, the engine temperature causes the bi-metallic strip to hold the valve in an open position.