Aurora V6-214 3.5L VIN H SFI (2001)
Idle Air Control Motor (IAC): Testing and Inspection
CIRCUIT DESCRIPTION
The Idle Air Control (IAC) valve is located in the throttle body of both the Throttle Bowl Injection (TBI) and the multi-port fuel injection (MFI)
Systems. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a
2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time the polarity of a winding is
changed. This change in polarity can be seen when observing a test lamp connected between ground or B+ and an IAC valve circuit while the PCM is
attempting to change engine RPM. The test lamp will flash ON or OFF each time the polarity is changed. The Powertrain Control Module (PCM)
does not use a physical sensor in order to determine the IAC pintle position, but uses a predicted number of counts. One count represents one change
in the polarity, which equals one step of the stepper motor. The PCM counts the steps it has commanded in order to determine the IAC pintle position.
The PCM uses the IAC valve in order to control the engine idle speed. The PCM does this by changing the pintle position in the idle air passage of the
throttle body. This procedure varies the air flow around the throttle plate when the throttle is closed. In order to determine the desired position of the
IAC pintle at idle or during deceleration, the PCM refers to the following inputs:
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The engine RPM
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The battery voltage
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The air temperature
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The engine coolant temperature
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The throttle position sensor angle
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The engine load
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The vehicle speed
When the ignition key is turned OFF after an ignition cycle, the PCM will first seat the IAC pintle in the air bypass bore and then retract the pintle a
predetermined number of counts in order to allow the proper amount of air to bypass the throttle plate for engine start-up. This procedure is known as
an IAC reset.
DIAGNOSTIC AIDS
Inspect for the following conditions:
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A skewed high Throttle Position (TP) sensor
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A restricted air intake system
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Objects blocking the IAC passage or the throttle bore
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A correct, properly-installed, and properly operating Positive Crankcase Ventilation (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 sensor, if equipped
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A throttle stop screw that shows evidence of damage or tampering
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A throttle shaft, a throttle linkage, or a cruise control linkage, if equipped, that show evidence of damage or tampering.
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Excessive deposits in the IAC passage or on the IAC pintle
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Excessive deposits in the throttle bore or on the throttle plate
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Vacuum leaks
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Excessive load on engine, from the. transmission, the power steering, the alternator, or from other equipment
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A high or unstable idle condition cam be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to Rough,
Unstable, or Incorrect/Idle and Stalling. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic
Procedures/Rough, Unstable, or Incorrect Idle and Stalling
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A low or unstable idle condition can be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to Rough,
Unstable, or Incorrect Idle and Stalling. See: Computers and Control Systems/Testing and Inspection/Symptom Related Diagnostic
Procedures/Rough, Unstable, or Incorrect Idle and Stalling
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If the problem is intermittent, refer to Intermittent Conditions in Symptoms. See: Computers and Control Systems/Testing and Inspection/Initial
Inspection and Diagnostic Overview/Diagnostic Strategies/Intermittent Conditions
TEST DESCRIPTION