Idle/Throttle Speed Control Unit: Description and Operation

The Idle Speed Control (ISC) unit controls idle speed using a plunger to change throttle angle. Idle speed is monitored by the Electronic Control Module (ECM) which moves the plunger to maintain idle speed required for the operating condition. The throttle switch, integral with the ISC, determines when the ISC controls idle speed. When throttle lever rests against ISC plunger, the switch contacts are closed and the ECM moves ISC to predetermined idle speed position. When throttle lever breaks contact with ISC plunger, the ECM stops sending idle speed commands and engine speed is controlled by the accelerator pedal.