Mystique L4-122 2.0L DOHC VIN 3 SFI (1995)
Idle Air Control (IAC) Valve: Description and Operation
PURPOSE
The Idle Air Control (IAC) solenoid allows the Powertrain Control Module (PCM) to accurately control engine idle speed under a variety of
conditions. The IAC solenoid is driven by an output signal from the PCM and allows intake airflow to bypass the throttle plates.
In addition to normal idle speed control the IAC solenoid also functions as a deceleration dashpot and allows for idle speed changes during periods
of increased engine load (A/C, electrical).
The IAC solenoid also plays an integral role in Adaptive Strategy correction. The PCM monitors the engine condition and adjusts the IAC
calibration to correct for wear and aging of components.
NOTE: Whenever an IAC component is replaced or cleaned it is recommended that the Keep Alive Memory (KAM) be be cleared. The vehicle
may exhibit idle concerns until new adaptive values are learned.
CONSTRUCTION
A duty cycle driven solenoid is directly linked to a reverse seated pintle valve.
Hitachi Idle Air Control (IAC) Valve And Solenoid
Hitachi With Vent/Filter
This type of IAC solenoid is not serviceable and cannot be cleaned.
Idle Air Control Solenoid
OPERATION
The IAC solenoid receives a 12 volt signal from circuit VPWR. The ground supply to the IAC solenoid is controlled by the PCM. The PCM
controls the amount of IAC operation by varying the duty cycle of the ground signal.
The IAC solenoid is linked directly to a pintle valve which controls the amount of intake airflow allowed to bypass the throttle plates.
RELATED DIAGNOSTIC TROUBLE CODES
DTC 412 Indicates that during the Key On Engine Running (KOER) self-test, engine rpm could not be controlled within the self-test limit band.
DTC 415 Indicates the IAC adaptive learning has reached the minimum learning limit (the valve is reducing air flow as much as possible).
DTC 416 Indicates the IAC adaptive learning has reached the maximum learning limit (the valve is admitting as much air flow as possible).
NOTE: Idle speed surging commonly results when the IAC solenoid reaches the limits of its operation. The IAC solenoid cannot compensate for
the required change in idle speed which results in the engine surging between the upper and lower limits of the IAC system.