Auxiliary Air Valve (Idle Speed): Description and Operation

Fast Idle Air Valve
The fast idle air valve consists of a thermo-wax pellet (2), springs (4) and a valve (5) and is located in the throttle body (1). When the engine is cold (Engine Coolant Temperature [ECT] sensor is lower than 70° C [158° F]), the thermo-wax pellet contracts. In this state, the valve opens by the spring force, allowing the air to be drawn into the intake manifold (4). The amount of air drawn into the intake manifold will increase even though the throttle valve remains at the idle position The engine speed will rise to the fast idle state which is higher than the idle speed.

When the engine warms up, the thermo-wax pellet gradually expands, the piston pushes down the valve gradually, and the amount of air passing through the fast idle air valve decreases as does the engine speed. When the ECT reaches about 70° C (158° F), the valve is fully closed and the engine speed returns to the normal idle speed.