Idle Speed/Throttle Actuator - Electronic: Description and Operation

PURPOSE
The Idle Air Control Bypass Air (IAC BPA) valve consists of the Bypass Air (BPA) valve and the Idle Air Control (IAC) valve. The BPA valve functions during cold engine operation to increase engine idle speed. The BPA valve consists of a thermowax bead and valve.

FEATURES
In order to ensure idle smoothness for all operating conditions, the IAC BPA valve controls the amount of air bypassing the throttle valve. In order to maintain factory-set idle speed when the engine is cold, air also flows through the IAC BPA valve during all modes of engine operation.





OPERATION
Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation (below 60°C [140°F]) the thermowax is contracted enough to allow the air valve to open. As the engine coolant directed around the thermowax heats, the thermowax begins to expand. When the engine coolant reaches temperatures above 60°C (140°F), the thermowax expands and closes the air valve.