K 2500 Suburban 4WD V8-454 7.4L (1994)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
Idle Air Control (IAC) Circuit
OPERATION:
All engine idle speeds are controlled by the control module through the Idle Air Control (IAC) valve mounted on the throttle body. The control
module sends voltage pulses to the IAC motor windings causing the IAC motor shaft and pintle to move in and out a given distance (number of
steps) for each pulse, (called counts).
This movement controls airflow around the throttle plate, which in turn controls engine idle speed, either cold or hot. IAC pintle position counts
can be seen using a "Scan" tool. 0 counts correspond to a fully closed passage, while 140 counts or more (depending on application) corresponds
to full airflow through the throttle body bypassing the throttle blade.