Idle/Throttle Speed Control Unit: Description and Operation

PURPOSE
On some models, idle speed is controlled by the Idle Speed Control (ISC) motor and ISC throttle switch.

ISC Motor Operation
The ECM monitors engine load--MAP--and engine speed--rpm--to determine the proper throttle opening.

The ECM then regulates engine speed by transmitting voltage signals to the ISC motor--opening or closing the throttle plates.

ISC Switch Operation
The ISC switch--mounted on the ISC motor housing--is closed when the ISC plunger contacts the throttle lever, and opens as the lever moves away from the plunger.
- When the switch contacts are closed the ISC motor controls idle speed.
- When the switch contacts are open the ISC plunger cannot retract.