For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provide an overview of each diagnostic category.

### DTC Descriptors

DTC P0506: Idle Speed Low
DTC P0507: Idle Speed High

### Circuit/System Description

The engine control module (ECM) controls the engine idle speed by adjusting the position of the idle air control (IAC) valve pintle. The IAC valve is a stepper motor driven by two internal coils. The movement of the IAC valve is controlled electrically by four circuits. Drivers within the ECM control the polarity of the 2 windings inside the IAC valve through these circuits. The ECM, by commanding the correct polarity in sequence, is able to command the motor within the IAC valve to rotate clockwise or counterclockwise in steps. In order for the armature of the stepper motor of the IAC valve to turn 1 revolution, it needs to move approximately 24 steps. The IAC valve motor is linked by a gear drive to the IAC valve pintle. The electrical pulses sent to the IAC valve coils, by the ECM, allows the pintle to extend or retract into the passage in the throttle body. By retracting the pintle, air is allowed to bypass the throttle valve, which will increase air flow and raise engine speed. When the pintle is extended, bypass air is decreased which lowers engine speed. IAC valve movement is measured in counts on the scan tool. Each count is equivalent to a step of the IAC valve. When the IAC valve is fully extended, and seated in the throttle body bore, the scan tool displays zero and the engine speed is slow. As the IAC valve pintle retracts the counts will raise along with engine speed.

The IAC valve the following circuits:

• | An IAC Coil A High

• | An IAC Coil A Low

• | An IAC Coil B High

• | An IAC Coil B Low

### IAC Valve Reset

When the ignition switch is turned OFF for more than 10 seconds an IAC valve reset occurs. At that time, the ECM commands the IAC valve to extend for a certain period which allows the IAC pintle to seat in the throttle body bore. This position is then sensed as zero count position for the IAC valve by the ECM. It must be observed that the IAC valve position is only sensed by the ECM measuring counts or steps of the driver circuit, there is no direct sensing of its exact position. When this extend time period ends, the ECM then commands the IAC valve to retract a predetermined amount. This will allow for a high engine speed on the next ignition cycle. If for any reason the IAC valve pintle moves after this reset, before the next ignition cycle, the ECM will not be able to detect it and will affect the ability to control engine idle. When the IAC valve is removed for any reason the reset must be performed.

### Conditions for Running the DTC

• | DTCs P0106, P0107, P0108, P0112, P0113, P0115, P0116, P0117, P0118, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0337, P0341, P0342, P0351, P0352, P0402, P0404, P0405, P0406, P042E, P0443, P0502, P1133, P1134, P1167, and P2297 are not set.

• | The engine run time is greater than 60 seconds.

• | The evaporative emission (EVAP) purge flow is less than 100 percent.

• | The barometric pressure (BARO) is greater than 72 kPa.

• | The intake air temperature (IAT) is greater than -20°C (-4°F).

• | The engine coolant temperature (ECT) is greater than 60°C (140°F).

• | The ignition voltage is between 11-16 volts.

• | The manifold absolute pressure (MAP) is between 22-60 kPa.

• | The DTCs run continuously when the above conditions are met for 5 seconds.

### Conditions for Setting the DTC

#### P0506

The actual engine speed is 100 RPM less than the desired idle speed by for 10 seconds.

#### P0507

The actual engine speed is 200 RPM more than the desired idle speed for 10 seconds.

### Action Taken When the DTC Sets

DTCs P0506, and P0507 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0506, and P0507 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Raise the engine speed to 2,500 RPM for 30 seconds and then allow the engine to idle for 3 minutes. DTCs P0506 or P0507 should not set.
2. If the vehicle passes the Circuit/System Verification test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the IAC valve.

Important: The ECM controls the IAC control circuits in pairs. One pair will be grounded, while the other pair is supplied a voltage.

2. Ignition ON, probe all of the IAC harness connector terminals with a test lamp connected to B+. The test lamp should illuminate on one pair of the following terminals:

• | Terminals A and D

• | Terminals B and C

⇒ | If the test lamp illuminates on a circuit other than a circuit in the pair, test the isolated circuit for a short to ground. If the circuit/connections test normal, replace the ECM.

⇒ | If the test lamp does not illuminate on both circuits in the pair, test the applicable IAC control circuit of the IAC valve for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.

3. Probe all of the IAC harness connector terminals with a test lamp connected to ground. The test lamp should illuminate on one pair of the following terminals:

• | Terminals A and D

• | Terminals B and C

⇒ | If the test lamp does not illuminate on both circuits in the pair, test the applicable IAC control circuit of the IAC valve for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.

4. Ignition OFF for 20 seconds. Ignition ON, repeat steps 2 and 3 in order to verify that all circuits test OK.
5. If all circuits test normal, inspect for the following:

• | A clogged IAC passage

• | Excessive deposits on the throttle plate or bore

• | Excessive deposits on IAC valve pintle or bore

• | Restricted air intake system

• | The throttle body for damage and/or tampering

• | Vacuum leaks

• | Malfunctioning PCV valve

6. If all conditions test normal, test or replace the IAC valve.

### Component Testing

1. Test for 40-80 ohms of resistance between the following terminals of the IAC valve.

• | A and B

• | C and D

⇒ | If the resistance is not within the specified range, replace the IAC valve.

2. Test for infinite resistance between the following terminals of the IAC valve.

• | A and C

• | B and C

⇒ | If less than the specified range, replace the IAC valve.

3. Test for infinite resistance between each terminal of the IAC valve, and the housing of the IAC valve.

⇒ | If less than the specified range, replace the IAC valve.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Idle Air Control Valve Replacement

• | Control Module References for ECM replacement, setup, and programming