Idle/Throttle Speed Control Unit: Description and Operation

Throttle Body Assembly:

ISC Airflow Diagram:

DESCRIPTION
The Idle Speed Control (ISC) motor is mounted on the throttle body with a bracket and is used to control engine idle speed. The ISC plunger acts as a movable throttle stop.
The PCM monitors engine idle speed through the Ignition Control (IC) module and moves the ISC plunger (throttle stop) to maintain the desired idle speed.
An integral part of the ISC motor is the Throttle Position (TP) switch (which is different from the TP sensor). When the throttle lever rests against the ISC plunger, the TP 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 TP switch contacts open, indicating to the PCM to stop controlling idle speed.
A faulty ISC motor TP switch can cause various driveability conditions. The TP switch is an integral part of the ISC motor and cannot be serviced separately.