Circuit Description
The powertrain control module (PCM) controls the air entering into the engine with an idle air control (IAC) valve. To increase the idle RPM, the PCM commands the pintle inside the IAC valve away from the throttle body seat. This allows more air to bypass through the throttle blade. To decrease the RPM the PCM commands the pintle towards the throttle body seat. This reduces the amount of air bypassing the throttle blade. A scan tool will read the IAC valve pintle position in counts. The higher the counts, the more air that is allowed to bypass the throttle blade.
Conditions for Setting
| • | The IAC valve reads less than 2 counts on the scan tool. |
| • | The barometer is less than 72 kPa. |
| • | The ECT sensor indicates temperature greater than 40°C (104°F). |
| • | The idle speed deviates below desired RPM by greater than 60 RPM for greater than 5 seconds. |
| • | The engine run time is greater than 20 seconds. |
| • | The TP angle is less than 1 percent. |
| • | One or more of the following DTCs are not set: P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P131, P0132, P0133, P0134, P0200, P0325, P0335, P0341, P0342, P0400, P0401, P0402, P0441, P0502, P0503, P562, P0563, P0600, P0601, P0602, P0712, P0713, P0716, P0717, P0741, P0742, P0748, P0751, P0753, P0756, P0758, P1441, P1520, P1810, P1811, P1812, P1860, P1864, P1870, P1871, P1887. |
Action Taken
Malfunction indicator lamp (MIL) will illuminate after two consecutive drive cycles have occurred with a fault.
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
| • | Inspect the IAC valve electrical connection for proper mating. |
| • | Inspect the wiring harness for damage. |
| • | Inspect the throttle stop screw for signs of tampering. |
| • | Inspect the throttle linkage for signs of bindings or excessive wear. |
| • | A slow or unstable idle may be caused by one of the following conditions: |
| - | Fuel system too rich or too lean |
| - | Foreign material in the throttle body bore or in the air induction system |
| - | A leaking or restricted intake manifold |
| - | Excessive engine overloading--Check for seized pulleys, pumps, or motors on the accessory drive. |
| - | Overweight engine oil |
| - | Refer to Rough, Unstable, or Incorrect Idle and Stalling . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
2 |
Does the engine RPM change smoothly when commanded by the scan tool? | 80°C (176°F) 900-2,500 RPM | Go to Step 3 | Go to Step 5 |
3 |
Are the resistance's across terminals A and B and terminals C and D within the specified range? | 40-80ohms | Go to Step 4 | Go to Step 7 |
4 |
Is the resistance across terminals B and C and terminals A and D infinite? | -- | Go to Diagnostic Aids | Go to Step 7 |
5 |
Does the node light change when the valve is being cycles? | -- | Go to Step 6 | Go to Step 8 |
6 | Inspect the IAC valve electrical connector for proper mating. Repair or replace as necessary. Is a repair necessary? | -- | Go to Step 7 | |
7 |
Is the repair complete? | -- | Go to Diagnostic Aids | |
8 |
Was a problem found and corrected? | -- | Go to Step 9 | |
9 |
Is the action complete? | -- | -- | |
