Idle Speed/Throttle Actuator - Electronic: Description and Operation

PURPOSE
The Idle Speed Control Bypass Air (ISC-BPA) valve is a component of the idle speed control system. It regulates the amount of intake air allowed to bypass the throttle valve in accordance with engine coolant temperature and signals sent by the Powertrain Control Module (PCM).

CONSTRUCTION
The ISC-BPA valve is composed of two separate elements. The ISC is a duty cycle solenoid which is operated by the PCM. The BPA is a thermowax type valve that responds to changes in engine coolant temperature.

OPERATION
During cold engine operation the BPA allows additional airflow to bypass the throttle plate to increase the idle speed. As the coolant warms up the thermowax bulb in the BPA expands and shuts off the airflow. The PCM then begins to control idle speed by varying the duty cycle to the ISC.