Auxiliary Air Valve (Idle Speed): Description and Operation

Fast Idle Air Valve:

FAST IDLE AIR VALVE

DESCRIPTION
The fast idle air valve consists of thermo-wax, springs and a valve.

OPERATION
Cold Engine
When the engine is cold (Engine Coolant Temperature [ECT] is lower than 70°C [158°F]), the thermo-wax contracts. In this state, the valve opens by the spring force, allowing the 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 rises to the fast idle state which is higher than the idle speed.

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