Idle Speed Control System

Idle Air Control (IAC) System:

PURPOSE
The Idle Air Control System allows for precise control of the engine idle during cold, warm and high load conditions.

Idle Air Adjusting (IAA) Unit:

LOCATION
ECM is on the floor, behind the center console. Idle Control Unit and Air Regulator is on the intake manifold.

OPERATION
Idle speed is controlled by fine adjustment of the amount of air allowed to bypass the throttle valve.

Three different devices, all part of the Idle Control System, are used to control engine idle. The devices are:

1. Idle Air Control Valve-Air Regulator (IACV-Air Reg)
^ Used to provide additional by-pass air during cold engine operation. Allows cold fast idle. Is activated by 12 VDC.
2. Idle Air Control Valve-Fast Idle Control Device (IACV-FICD).
^ Used to provide a small amount of idle-up when the A/C compressor is turned on. Is activated by 12 VDC.
3. Idle Air Control Valve-Auxiliary Air Control (IACV-ACC) Valve.
^ Used to provide fine control of the engine idle during normal conditions. Is activated by a duty cycle signal from the ECM at a rate of 100 - 200 Hz.