K Yukon/Denali 4WD V8-5.7L VIN R (2000)
Idle Air Control Motor (IAC): Description and Operation
Throttle Body Assembly
The purpose of the IAC valve assembly is to control the engine idle speed while preventing engine stalls due to changes in the engine load. The IAC
valve (1), mounted in the throttle body assembly, controls the bypass air around the throttle valve (2). By moving a conical valve known as a pintle (3) in
toward the seat, in order to decrease the air flow, or out away from the seat, in order to increase the air flow, a controlled amount of air moves around the
throttle valve. If the engine speed is too low, more air is bypassed around the throttle valve in order to increase the RPM. If the engine speed is too high,
less air is bypassed around the throttle valve in order to decrease the RPM. The control module moves the IAC valve in small steps, called counts. These
can be displayed by a scan tool, which plugs into the Data Link Connector (DLC).
The control module calculates the proper position of the IAC valve during idle based on the battery voltage, the engine coolant temperature, the engine
load, and the engine RPM. If the RPM drops below specification and the throttle valve is closed, the control module senses a near stall condition and
calculates a new valve position in order to prevent stalling.
