Auxiliary Air Valve (Idle Speed): Description and Operation

By-Pass Air (BPA) Valve:

PURPOSE
The By-Pass Air (BPA) valve increases idle speed during cold engine conditions to speed engine warm-up and prevent cold engine stalling.

OPERATION
The valve consists of a thermowax material that expands or contracts depending on engine coolant temperature. It opens below 104°F (40°C) to allow bypass air to flow into the intake plenum. Above that temperature, the valve remains closed.