For 1990-2009 cars

### Circuit Description

The idle air control (IAC) valve is located in the throttle body of the sequential multiport fuel injection (SFI) system. It 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 battery positive voltage 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 in order 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 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. It 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:

• | Engine RPM

• | Battery voltage

• | Air temperature

• | Engine coolant temperature

• | Throttle position sensor angle

• | Engine load

• | 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 it 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, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0300, P0401, P0403, P0443, P1121, P1404, or P1441 are not set.

• | The engine run time greater than 2 minutes.

• | The engine coolant temperature (ECT) is greater than 70°C (158°F).

• | The intake air temperature (IAT) is greater than -18°C (0.4°F).

• | The barometric pressure (BARO) greater than 70 kPa.

• | The ignition voltage is between 9-18 volts.

• | The throttle position (TP) sensor less than 1.5 percent.

• | The vehicle speed sensor (VSS) less than 4.8 km/h (3 mph).

• | The above conditions are present for 5 seconds.

### Conditions for Setting the DTC

• | The actual engine speed is 50 RPM less than the desired engine speed.

• | The diagnostic must fail 4 consecutive tests per key cycle.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

Inspect for the following conditions:

• | A restricted air intake system

• | Proper operation and installation of all air intake components--Check for collapsed, clogged, or loose air intake ducts, a clogged air filter, and correct operation of the mass air flow 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 can be caused by a non-IAC system problem that cannot be overcome by the IAC valve. Refer to Symptoms - Engine Controls .

• | If the problem is intermittent, refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This test will determine the ability of the Engine Controller and IAC valve circuits to control the IAC valve.

2. 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.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Important: Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 100 RPM of the commanded RPM.

1. Set the parking brake and block the drive wheels.
2. Install a scan tool.
3. Start the engine.
4. Turn OFF all of the accessories.
5. With the scan tool RPM control function slowly increment engine speed to 1,800 RPM, then to 600 RPM, Then to 1,800 RPM.
6. Exit the RPM control function.

Does the engine speed stabilize within 100 RPM of the commanded RPM during the above test?

Go to Step 3

Go to Step 4

3 |

1. Observe the Freeze Frame/Failure Records data for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the IAC valve.
3. Connect a J 37027-A IAC motor driver to the IAC valve.
4. Start the engine.
5. With the J 37027-A , command the IAC valve in until near 600 RPM is reached.
6. With the IAC motor driver, command the IAC valve out until near 1,800 RPM is reached.
7. Return engine speed to desired idle as indicated on the scan tool data list.

Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1,800 RPM when the IAC valve was commanded in and out?

Go to Step 5

Go to Step 11

5 |

1. With a test lamp connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using the J 35616 connector test adapter kit .
2. Start the engine.
3. With the IAC motor driver, command low RPM while observing a scan tool until the IAC counts start to increment.
4. With the IAC motor driver, command high RPM while observing a scan tool until the IAC counts start to increment.
5. While the IAC counts are incrementing observe the test lamp.
6. Return engine idle speed to desired idle as indicated on the scan tool data list.
7. Repeat the above procedure for the other three IAC valve circuits.

Did the test lamp remain ON (never flashing) while the IAC counts where incrementing at any of the IAC valve circuits during the above test?

Go to Step 10

Go to Step 6

6 | Did the test lamp remain OFF (never flashing) while the IAC counts where incrementing at any of the IAC valve circuits during the above test? | Go to Step 9 | Go to Step 7
7 |

1. Connect a test lamp between the IAC coil A low circuit and the IAC coil A high circuit at the IAC valve harness connector using the J 35616 connector test adapter kit.
2. With the IAC motor driver, command low RPM while observing a scan tool until the IAC counts start to increment.
3. With the IAC motor driver, command high RPM while observing a scan tool until the IAC counts start to increment.
4. While the IAC counts are incrementing, observe the test lamp.
5. Return engine idle speed to desired idle as indicated on the scan tool data list.
6. Repeat the above procedure with the test lamp connected between the IAC coil B low circuit and the IAC coil B high circuit at the IAC valve harness connector.
7. Return engine speed to the desired idle as indicated on the scan tool data list.

Did the test lamp stay illuminated (never flashing) while the IAC counts where incrementing during the above test?

Go to Step 8

Go to Step 15

8 | Inspect for a poor connection at the IAC valve harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 16 | Go to Diagnostic Aids
9 |

1. Turn OFF the ignition.
2. Disconnect the PCM harness connectors.
3. With a DMM, test for an open or short to ground on the IAC valve circuit where the test lamp remained OFF. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 12

10 |

1. Turn ON the ignition.
2. With a DMM, test for a short to voltage on the IAC valve circuit where the test lamp remained illuminated. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 12

11 |

1. Visually/Physically inspect for the following:

• | Throttle body damage and tampering--Throttle lever screw tampering, if equipped

• | Restricted air intake system--Inspect for a possible collapsed/clogged air intake duct (before and after the air filter element), restricted air filter element, restriction at the throttle body intake screen (if equipped).

2. Remove the IAC valve. Refer to Idle Air Control Valve Replacement .
3. Inspect for the following conditions:

• | Clogged IAC passage

• | Excessive deposits on the throttle plate

• | Excessive deposits in the throttle bore

• | Excessive deposits on IAC valve pintle

4. Repair any of the above conditions as necessary. Refer to the appropriate repair procedure.

Did you find and correct the condition?

Go to Step 16

Go to Step 13

12 | Inspect for a poor connection at the PCM harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 16 | Go to Step 15
13 | Inspect for a poor connection at the IAC valve harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 16 | Go to Step 14
14 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Did you complete the replacement? | Go to Step 16 | --
15 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 16 | --
16 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 17

Go to Step 2

17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK