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Idle Speed Control (ISC) (CARBURETED Models)

The ISC is a motor which opens or closes the throttle (in idle position), according to commands from the ECM. The ISC maintains low idle speeds while preventing stalling due to engine load. The base idle speed is programmed into ECM memory and is not adjustable.

When the engine is cold, ECM holds the throttle valve open for a longer period of time to provide faster warm-up. This function is by-passed when throttle is opened enough to bring TPS off its idle circuit.

NOTE: Not all engines are equipped with ISC system. Some may use an Idle Speed Solenoid (ISS) or an Idle Load Compensator (ILC) to control engine idle speed without ECM commands.
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