Idle Speed: Testing and Inspection

Throttle/Idle Learn

Description

The engine control module (ECM) learns the airflow through the throttle body to ensure the correct idle. The learned airflow values are stored within the ECM. These values are learned to adjust for production variation and will continuously learn during the life of the vehicle to compensate for reduced airflow due to throttle body coking. Anytime the throttle body airflow rate changes, for example due to cleaning or replacing, the values must be relearned.

An engine that had a heavily coked throttle body that has been cleaned or replaced may take several drive cycles to learn out the coking. To accelerate the process, the scan tool has the ability to reset all learned values back to zero. A new ECM will also have values set to zero.

The idle may be unstable or a DTC may set if the learned values do not match the actual airflow.

Conditions for Running the Throttle Learn Procedure

Reset Procedure
* DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0128, P0171, P0172, P0174, P0175, P0201-P0206, P0222, P0223, P0300-P0306, P0351-P0356, P0496, P0506, P0507, P0601-P0604, P0606, P062B, P062F, P0630, P0641, P0651, P0697, P06A3, P1101, P1516, P2101, P2119, P2122, P2123, P2127, P2128, P16F3, P2135, P2138, P2176, or P2610 are not set.
* Ignition ON, engine OFF.
* The vehicle speed sensor (VSS) is 0 km/h (0 mph).

Learn Procedure
* DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0121, P0122, P0123, P0128, P0171, P0172, P0174, P0175, P0201-P0206, P0222, P0223, P0300-P0306, P0351-P0356, P0496, P0506, P0507, P0601-P0604, P0606, P062B, P062F, P0630, P0641, P0651, P0697, P06A3, P1101, P1516, P2101, P2119, P2122, P2123, P2127, P2128, P16F3, P2135, P2138, P2176, or P2610 are not set.
* The engine speed is between 450-4,000 RPM.
* The manifold absolute pressure (MAP) is greater than 5 kPa.
* The mass air flow (MAF) is greater than 2 g/s.
* The ignition voltage is greater than 11 V.

Reset/Learn Procedure

Reset Procedure - Performed after the throttle body is cleaned or replaced
1. Ignition ON, engine OFF, perform the Idle Learn Reset in Module Setup with a scan tool.
2. Engine idling, monitor the Throttle Body Idle Airflow Compensation parameter. The Throttle Body Idle Airflow Compensation value should equal 0 % and the engine should be idling at a normal idle speed.
3. Clear the DTCs and return to the diagnostic that referred you here.

Learn Procedure - Performed after the ECM is programmed or replaced

Note: Do NOT perform this procedure if DTCs are set. Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

1. Engine idling for 3 minutes.
2. Monitor the Desired Idle Speed and the actual Engine Speed with a scan tool.
3. The ECM will start to learn the new idle cells and Desired Idle Speed should start to decrease.
4. Ignition OFF for 60 s.
5. Engine idling for 3 minutes.
6. After the 3 minute run time the engine speed should return to normal.

Note: During the drive cycle monitor the DTC information with a scan tool to verify DTC P0506 and P0507 do not set. If DTC P0506 and P0507 set, clear the DTCs so the ECM can continue to learn.

• If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.

7. After the drive cycle, the engine speed should return to normal.

• If the engine idle speed has not been learned, turn OFF the ignition for 60 s and repeat step 6.

8. Once the engine speed has returned to normal, clear DTCs and return to the diagnostic that referred you here.