Auxiliary Air Valve (Idle Speed): Description and Operation

Fast Idle Thermo Valve and Idle Air Control (IAC) Valve:

PURPOSE
Raises the idle speed when the engine is cold.

CONSTRUCTION
Aluminum housing with passages for coolant to flow through and around a thermowax plunger, controlling air flow through the throttle body bypass.

OPERATION
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.