GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Idle Speed Control (ISC)


See Figure 1

The idle speed control does just what its name implies-it controls the idle. The ISC is used to maintain low engine speeds while at the same time preventing stalling due to engine load changes. The system consists of a motor assembly mounted on the carburetor which moves the throttle lever so as to open or close the throttle blades.

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Fig. Fig. 1: The idle speed control motor (ISC) is mounted on the side of the carburetor

The whole operation is controlled by the ECM/PCM. The ECM/PCM monitors engine load to determine the proper idle speed. To prevent stalling, it monitors the air conditioning compressor switch, the transaxle, the park/neutral switch and the ISC throttle switch. The ECM/PCM processes all this information and then uses it to control the ISC motor which in turn will vary the idle speed as necessary.