Idle Air Control (IAC) Valve Circuit

IAC Valve Circuit

System Schematic:

CIRCUIT DESCRIPTION
The IAC valve is situated on the intake air chamber Intake air bypassing the throttle valve is directed to the IAC valve through a passage.

A step motor is built into the IAC valve. It consists of 4 coils, a magnetic rotor, valve shaft and valve. When current flows to the coils due to signals from the ECM, the rotor turns and moves the valve shaft forward or backward, changing the clearance between the valve and the valve seat.

In this way the intake air volume bypassing the throttle valve is regulated, controlling the engine speed. There are 125 possible positions to which the valve can be opened.

Reference INSPECTION USING OSCILLOSCOPE
- With the engine idling measure waveforms between terminals ISC1, ISC2, ISC3, ISC4 and EO1 of engine control module with A/C switch On or OFF.

Reference Waveform IAC Valve Open:

Reference Waveform IAC Valve Close:

HINT:The correct waveforms are as shown.





WIRING DIAGRAM

Step 1:

Step 2:

INSPECTION PROCEDURE