Idle/Throttle Speed Control Unit: Description and Operation

Throttle Body Assembly:

The Idle Speed Control (ISC) Actuator is mounted on the throttle body with a bracket and is used to control engine idle speed. The ISC plunger acts as a moveable throttle stop. The Powertrain Control Module (PCM) monitors engine idle speed through the Ignition Control Module (ICM) and moves the ISC plunger to maintain the desired idle speed.

An integral part of the ISC Actuator is the throttle switch (which is different from the Throttle Position (TP) sensor). When the throttle lever rests against the ISC plunger, the throttle switch contacts close, indicating to the PCM that it should control idle speed. When the throttle lever is lifted off of the ISC plunger, such as when the accelerator pedal is depressed, the throttle switch contacts open, indicating to the PCM to stop controlling idle speed.

A faulty ISC Actuator or throttle switch can cause various driveability conditions. The throttle switch is an integral part of the ISC Actuator and cannot be serviced separately.