Fast idle thermo valve

After the engine starts, the IAC valve opens for a certain time. The amount of air is increased to raise the idle speed about 150 – 300 rpm.

When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to the engine coolant temperature.

Fast idle thermo valve

A Fast idle thermo valve

B IAC valve

A Air bypass valve

B Wax

To Prevent erratic running when the engine is warming up, it is necessary to raise the idle speed. The fast idle thermo valve is controlled by a thermowax plunger. When the engine is cold, the engine coolant surrounding the thermowax contracts the plunger, allowing additional air to be bypassed into the intake manifold so that the engine idles faster. As the engine temperature rises the thermowax expands pushing the plunger and reducing the amount of bypassing into the intake manifold.