Auxiliary Air Valve (Idle Speed): Description and Operation

Opening Air Valve:

The air valve consists of thermo-wax, springs and a valve. When the engine is cold (or engine coolant is lower than about 60°C [140°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.

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