Monte Carlo V6-262 4.3L (1986)
Fig. 034 Chart C-2C Idle Air Control
The ECM will control engine idle speed by moving the IAC valve to control air flow around the throttle plate. It does this by sending voltage pulses to
the proper motor winding for IAC motor. This will cause the motor shaft and valve to move "IN" or "OUT" of the motor a given distance for each pulse
received. ECM pulses are referred to as "counts".
a. To increase idle speed - ECM will send enough counts to retract the IAC valve and allow more air to flow through the idle air passage and
bypass the throttle plate until idle speed reaches the proper RPM. This will increase the ECM counts.
b. To decrease idle speed - ECM will send enough counts to extend the IAC valve and reduce air flow through the idle passage around the
throttle plate. This will reduce the ECM counts.
Each time the engine is started and then the ignition is turned off the ECM will reset the IAC valve. This is done by sending enough counts to seat the
valve. The fully seated valve is the ECM reference Zero. A given number of counts are then issued to open the valve, and normal ECM control of IAC
will begin from this point. This is how the ECM knows what the motor position is for a given idle speed.
The ECM uses the following information to control idle speed.
a. Battery voltage
