Savana 1/2 Ton Van V8-5.7L VIN R (2001)
Idle Speed: Adjustments
STANDARD MODELS (NON-ALTERNATIVE FUELS)
CIRCUIT DESCRIPTION
The Idle Air Control (IAC) valve is located in the throttle body of both Sequential Multiport Fuel Injection (SFI) and Multiport 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
two 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 to determine IAC pintle position, but uses a predicted number of counts. One count represents one change in polarity
which equals one step of the stepper motor. The PCM counts the steps the PCM has commanded to determine IAC pintle position. The PCM uses the
IAC valve to control engine idle speed. The PCM does this by changing the pintle position in the idle air passage of the throttle body. This varies the
air flow around the throttle plate when the throttle is closed. To determine the desired position of the IAC pintle at idle or during deceleration, the
PCM refers to the following inputs:
^
The engine RPM
^
The battery voltage
^
The air temperature
^
The Engine Coolant Temperature (ECT)
^
The Throttle Position (TP) sensor angle
^
The engine load The vehicle speed
