P0506

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 Idle Air Control (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 Powertrain Control Module (PCM) is attempting to change engine RPM. The test lamp will flash ON or OFF each time the polarity is changed. The 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

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 IAC pintle a predetermined amount of counts to allow the proper amount of air to bypass the throttle plate for engine start-up. This procedure is known as an IAC Reset.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101-P0103, P0106-P0108, P0112, P0113, P0117, P0118, P0121-P0123, P0125, P0128, P0171, P0172, P0174, P0175, P0200, P0300, P0440, P0442, P0443, P0446, P0449, P1111, P1112, P1114, P1115, P1121, P1122, P1380, P1381, or P1441 are not set.
^ The engine run time is more than 60 seconds.
^ The Engine Coolant Temperature (ECT) is more than 60°C (140°F).
^ The Intake Air Temperature (IAT) is more than -10°C (14°F).
^ The Throttle Position (TP) sensor is less than 0.7 percent.
^ The Barometric Pressure (BARO) is more than 65 kPa.
^ The Vehicle Speed Sensor (VSS) is less than 1.6 km/h (1 mph).
^ The ignition voltage is between 9-18 volts.
^ The above conditions are present for 2 seconds.

CONDITIONS FOR SETTING THE DTC
The actual engine speed is 100 RPM less than the desired engine speed.

DIAGNOSTIC AIDS
Inspect for the following conditions:
^ A restricted air intake system
^ Proper operation and installation of all air intake components, such as collapsed, clogged, or loose air intake ducts, clogged air filter, proper operation of the Mass Air Flow (MAF) sensor, if equipped
^ A tampered with or damaged throttle stop screw
^ A tampered with or damaged throttle plate, throttle shaft, or throttle linkage
^ Objects blocking the IAC passage or throttle bore
^ Excessive deposits in the IAC passage or on the IAC pintle
^ Excessive deposits in the throttle bore or on the throttle plate
^ Vacuum leaks
^ A low or unstable idle condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve.refer to Symptoms - Computers and Control Systems. Standard Model (Non-Alternative Fuels)
^ If the problem is determined to be intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-5:

Steps 6-12:

Steps 13-16:

The numbers below refer to the step numbers on the diagnostic table.
5. This test will determine the ability of the engine controller and IAC valve circuits to control the IAC valve.
7. This test will determine the ability of the PCM to provide the IAC circuits with a ground. On a normally operating system, the test lamp should not flash while the IAC counts are incrementing.