Fast Idle Mechanism

Fig. 9 Typical fast idle mechanism:

The air bypass valve is controlled by a thermowax plunger, Fig. 9. When the thermowax is cold, the valve is open. When the thermowax is heated, the valve is closed. When the engine is cold the valve allows additional air to bypass into the intake manifold so that engine idles faster than normal. When engine reaches normal operating temperature, the valve begins to close, reducing amount of air bypassing into the intake manifold.