Auxiliary Air Valve (Idle Speed): Description and Operation

Fast Idle Air Valve:

The fast idle air valve consists of thermo-wax, springs and a valve. When the engine is cold (engine coolant temperature lower than 60 ° C (140 ° F), the thermo wax contracts. In this state, the valve opens by spring force, allowing air to be drawn into the intake manifold. Thus the amount of intake air increases even when the throttle valve is at the idle position and the engine speed raises to the fast idle state.

As the engine warms up, the thermo wax expands gradually, the piston pushes down on the valve gradually, and the amount of air that passing through the fast idle air valve decreases and so does engine speed. When the engine coolant temperature reaches 60 ° C (140 ° F), the valve is fully closed and the engine speed is back to normal idle speed.