OPERATION

The volume of intake air during engine idling is controlled by the opening and closing of the Idle Air Control (IAC) valve for bypassing the throttle valve, located at the air intake port. The DC motor turns clockwise or counter-clockwise according to the change in the direction of current in the motor drive IC inside the ECM. The IAC valve opens and closes depending on which direction the DC motor inside the IAC motor is turning.

While the engine is idling, if the idle speed and IAC valve position (step) change when the air conditioning switch is turned to On and Off, it can be assumed that the idle air control motor and the IAC valve position sensor are operating normally.

If the IAC valve position (step) is outside the standard position, the malfunction is probably one of the following:

• Basic idle speed adjustment is wrong.
• Some deposit is adhering to the throttle valve.
• Air is being drawn into the air intake manifold through a defective gasket seal.
• The EGR valve sheet adhesion is defective.
• Combustion malfunction inside a cylinder (spark plug, ignition coil, injector or compression pressure is defective.)

  Fig. 1: The location of the idle air control motor, attached to the throttle body — 2.4L (California, 1993 and later) engines