Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control (ISC) Valve:

The Idle Speed Control (ISC) Valve, located on the throttle body, is controlled by an ECU duty signal. The amount of bypass air allowed to flow around the throttle valve is precisely controlled by the ECU according to operating conditions sensed from several input devices, including:

Water thermosensor
Intake air thermosensor
Throttle sensor
Atmospheric pressure sensor
Neutral and clutch switches (M/T)
Inhibitor Switch (A/T)
A/C switch
Power steering pressure switch
Electrical load signal
Ignition switch ("START" position)
Distributor Ne signal (engine rpm)