K 1500 Yukon Denali AWD V8-6.0L VIN U (2002)
Idle Speed/Throttle Actuator - Electronic: Testing and Inspection
CIRCUIT DESCRIPTION
The engine idle speed is controlled by the idle air control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out
of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a two phase
bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called
steps. The stepper motor has two separate windings that are called coils. Each coil is fed by two circuits from the powertrain control module (PCM).
When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC
pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle
position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second,
the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a
calibrated period of time, an idle speed diagnostic trouble code (DTC) may set.
DIAGNOSTIC AIDS
Inspect for the following conditions:
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A skewed high throttle position (TP) sensor
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Restricted air intake system
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Objects blocking the IAC passage or throttle bore
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The correct positive crankcase ventilation (PCV) valve
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A properly installed PCV valve
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Proper operation of the PCV valve
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Proper operation and installation of all air intake components
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Proper installation and operation of the mass air flow (MAF) sensor, if equipped
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Evidence of damage or tampering of the following components:
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The throttle stop screw
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The throttle plate
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The throttle shaft
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The throttle linkage
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The cruise control linkage-if equipped
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Excess deposits in the IAC passage or on the IAC pintle
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Excess deposits in the throttle bore or on the throttle plate
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Vacuum leaks
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Excess load on engine, such as energy-draining conditions of the transmission, power steering, or alternator
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A high or unstable idle condition-This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. Refer
to Symptoms - Computers and Controls Systems. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic
Procedures
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A low or unstable idle condition-This condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. Refer
to Symptoms - Computers and Controls Systems. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic
Procedures
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An intermittent condition-If the condition is intermittent, refer to Intermittent Conditions. See: Computers and Control Systems/Testing and
Inspection/Initial Inspection and Diagnostic Overview/Intermittent Conditions
TEST DESCRIPTION
