Rodeo LS 4WD V6-3.2L (1998)
Idle Air Control Valve: Description and Operation
DESCRIPTION AND OPERATION
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 the conical valve (pintle) in (to decrease air flow) or
out (to increase air flow), a controlled amount of air can move around the throttle plate. If the RPM is too low, the Powertrain Control Module (
PCM) will retract the IAC pintle, resulting in more air moving past the throttle plate to increase the RPM. If the RPM is too high, the PCM will
extend the IAC pintle, allowing less air to move past the throttle plate, decreasing the RPM.
The IAC pintle valve moves in small steps called counts. During idle, the proper position of the IAC pintle 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, 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 must be reset. The
IAC resets when the key is cycled "ON" then "OFF." When servicing the IAC, it should only be disconnected or connected with the ignition
"OFF." The position of the IAC pintle valve affects engine start-up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too
much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. DTC P0507
or DTC P1509 may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with
possible hard starting and a rich air/fuel ratio. DTC P0506 or DTC P1508 may set. If the IAC pintle is stuck part-way open, the idle may be high
or low and will not respond to changes in the engine load.
