Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control (ISC) System:

Bypass Air Control (BAC) Valve:

The Bypass Air Control (BAC) Valve, located on the intake manifold near the throttle valve, is controlled by an ECU duty signal. With this type of control, the ECU can precisely regulate the volume of air allowed to bypass the throttle valve. Because the volume necessary to maintain smooth idle and good driveability varies with operating conditions, the ECU factors a number of inputs into its calculations for BAC valve control:

Intake air temperature
Coolant temperature
Engine speed
Throttle position
Electrical load
Gear selector position
Air conditioning
Power steering