Firebird V6-3.8L VIN K (1995)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
Figure C2-3 - IAC Valve
PURPOSE
The purpose of the Idle Air Control (IAC) valve is to control engine idle speed while preventing stalls due to changes in engine load. The IAC
valve, mounted in the throttle body, controls bypass air around the throttle plate. By moving a conical valve, known as a pintle, IN (to decrease air
flow) or OUT (to increase air flow), a controlled amount of air can move around the throttle plate.
OPERATION
If RPM is too low, the PCM will retract the IAC pintle resulting in more air being bypassed around the throttle plate to increase RPM. If RPM is
too high, the Powertrain Control Module (PCM) will extend the IAC pintle and allow less air to be bypassed around the throttle plate, decreasing
RPM.
The IAC pintle valve moves in small steps called "counts."
During idle, the proper position of the IAC pintle valve is calculated by the PCM based on battery voltage, coolant temperature, engine load, and
engine RPM. If the RPM drops below a specified value and the throttle plate is closed (Throttle Position (TP) sensor voltage is between
0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle valve position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.
The IAC resets when the ignition is turned ON, and then OFF.
When servicing the IAC, it should only be disconnected or connected with the ignition OFF. This will keep from having to reset the IAC.
The IAC pintle valve affects only the idle characteristics of the vehicle. If it is open fully, too much air will be allowed into the manifold and idle
speed will be high. If it is stuck closed, too little air will be allowed in the manifold, and idle speed will be too low. If it is stuck part way open, the
idle will be high and will not respond to changes in engine load.
