Auxiliary Air Valve (Idle Speed): Description and Operation

Fast Idle Valve:

The Fast Idle Valve, mounted on the throttle body next to the throttle angle (TPS) sensor, raises the idle speed when the engine is cold. The Fast Idle Valve is controlled by a thermowax plunger type valve. When the engine coolant is cold, the thermowax contracts the plunger which opens the valve allowing air to bypass the throttle plate and idle adjusting screw into the intake manifold. When the engine coolant warms up, the valve closes and the bypass air flow is blocked.