Auxiliary Air Valve (Idle Speed): Description and Operation

Idle Air Control Bypass Air (IAC BPA) Valve:

PURPOSE
The Idle Air Control Bypass Air (IAC-BPA) valve is a component of the idle speed control system. It regulates the amount of intake air allowed to bypass the throttle valve under a full range of operating conditions.

OPERATION
For improved cold engine running performance, the BPA valve supplies bypass air into the intake manifold to increase idle speed. As the engine warms up above 60°C (140°F), thermowax material expands, pushing the valve closed and reducing the bypass air flow amount. The valve responds to changes in the engine coolant temperature only, and is not electrically controlled by the Powertrain Control Module (PCM).

After warm-up, the Powertrain Control Module (PCM) controls the Idle Air Control (IAC) solenoid valve to maintain idle quality under various conditions.