DTC P0506: IAC System Rpm Low: Description

Idle Air Control (IAC) valve is located in throttle body of both SFI and MFI Systems. IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation, or movement, every time polarity of a winding is changed. This change in polarity can be seen when observing a test light connected between ground or battery voltage and an IAC valve circuit while Powertrain Control Module (PCM) is attempting to change engine RPM (test light will flash on or off each time polarity is changed). 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 stepper motor. PCM counts steps that have been commanded to determine IAC pintle position. PCM uses IAC valve to control engine idle speed. IAC valve does this by changing pintle position in idle air passage of throttle body. This varies airflow around throttle plate when throttle is closed. To determine the desired position of IAC pintle at idle or during deceleration, PCM refers to following inputs:

• Engine RPM
• Battery Voltage
• Air Temperature
• Engine Coolant Temperature
• Throttle Position Sensor Angle
• Engine Load
• Vehicle Speed

When ignition key is turned off after an ignition cycle, PCM will first seat IAC pintle in air by-pass bore and then retract pintle a predetermined amount of counts to allow proper amount of air to by-pass throttle plate for engine start-up. This procedure is known as an IAC reset.