Idle Speed Inspection. Chevrolet Metro 2001

For 1990-2009 cars

## Idle Speed Inspection w/o Scan Tool

The engine idle speed is controlled by the powertrain control module (PCM) through the idle air control (IAC) valve. The IAC valve opens and closes the idle air passage in the throttle body according to signals from the PCM. The PCM uses various information from sensors and from switches in order to determine the correct engine idle speed. The PCM increases the opening in the idle air passage when the engine speed drops below a specified value. The PCM maintains a smooth idle by monitoring certain engine components in order to respond to changes in engine load. The engine idle speed is a factory set calibration and is not adjustable.

1. Perform all of the following checks and operations:

• | Check the accelerator cable for free movement and for correct free-play. Refer to Accelerator Cable Adjustment .

• | Inspect the lead wires and the hoses of the sequential multiport fuel injection (SFI) and of the EVAP control systems for secure connections.

• | Turn off all of the accessories.

• | Verify that the air cleaner is installed correctly.

• | Check the air induction system for restrictions.

• | Check the vacuum hoses for correct routing. Refer to the Emission Label.

• | Check for and repair any vacuum leaks as necessary.

Important: Before starting the engine, place the automatic transaxle selector in Park, or place the manual transaxle control lever in neutral. Set the parking brake, and block the drive wheels.

2. Start the engine.
3. Run the engine to normal operating temperatures.
4. Connect a tachometer to the vehicle.
5. Access the duty check data link connector (8) that is located next to the PCM (7) behind the glove box.
6. Connect a fused jumper wire to the terminal 2 diagnostic switch and the terminal 4 ground of the connector.
7. Connect a DMM to the duty check terminal 6 and to the ground terminal 4 of the connector.
8. Select the DC voltage and the duty cycle (Hz) or dwell settings on the DMM.
9. Monitor the readings on the tachometer and on the DMM while turning ON the A/C.
10. Compare the observed engine speed and the observed IAC duty cycle with the values specified in the table.

• | If the indicated idle speed is not within the specified value, refer to Rough, Unstable, or Incorrect Idle and Stalling .

• | If the idle speed does not increase to the specified value when the A/C turns ON, refer to Air Conditioning (A/C) Idle Circuit Diagnosis .

• | Check the IAC valve and the IAC circuit for faults if the indicated IAC duty cycle is not within the specified value. Repair as necessary.

#### Idle Speed/IAC Duty Values

| A/C OFF | A/C ON
--- | --- | ---
Engine Speed | 700-800 RPM | 825-925 RPM
IAC Duty Cycle | 8%-25% *8%-35% | --
* High Altitude Only -- above 2 000 meters (6,560 feet)

## Idle Speed Inspection with Scan Tool

### Description

The powertrain control module (PCM) controls the engine idle speed through the idle air control (IAC) valve. The IAC valve opens and closes the idle air passage in the throttle body according to signals from the PCM. The PCM determines the correct engine idle speed by using information from various sensors and from various switches. The PCM increases IAC duty when engine speed drops below a specified value. The PCM maintains a smooth idle and a stable idle by monitoring certain engine components in order to respond to changes in engine load. The engine idle speed is a factory set calibration and is not adjustable.

### Diagnostic Aids

DO NOT attempt to adjust the IAC valve or the throttle-valve opening. The engine IAC valve and the idle speed are not adjustable. Operate the IAC valve with the scan tool by selecting the appropriate Output Control feature. Command the IAC valve to increase and to decrease the engine idle speed. Diagnose the faulty component, and replace the faulty component, or locate and repair the cause of the idle concern. Check for any of the following conditions if the IAC valve fails to control the engine speed when commanded by the scan tool:

• | Vacuum leaks

• | Blockage of the idle air passage

• | Incorrect PCV system operation

• | Excessive accessory engine loads

• | A faulty IAC valve

• | Faulty electrical connections in the IAC valve electrical circuit

If the engine idle speed is a concern when the air conditioning or the windshield defroster are running, check the A/C idle-up signal. Refer to Air Conditioning (A/C) Idle Circuit Diagnosis .

If the engine idle speed is a concern when the headlights, the blower motor, or the rear defogger are on, check the electrical load idle-up signal. Refer to Electrical/Accessory Load Idle-Up Signal Diagnosis .

### Test Description

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

1. The Powertrain OBD system check prompts the technician to complete some basic checks, and to store the applicable Freeze Frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool stores the information for later reference.

2. This step checks the engine idle speed with the engine at normal operating temperatures and without a load. DO NOT attempt to adjust the IAC valve or the throttle valve opening. The engine IAC valve and the idle speed are not adjustable. Locate the faulty component, and replace the faulty component, or repair the cause of the idle concern.

3. This step checks that the opening in the idle air passage of the IAC valve is within the expected percentage. A DTC P0505 may set if this parameter stays outside the specified value.

4. This step checks for vacuum leaks or for faulty connections in the fuel injection and in the EVAP control systems.

5. This step checks the accelerator control cable for a binding or for a condition that is adjusted incorrectly.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: Place the transmission gearshift control lever in the Neutral position, and apply the parking brake. Block the drive wheels.

1. Turn OFF all accessories.
2. Check that the air cleaner is correctly installed.
3. Start the engine.
4. Run the engine until normal operating temperature.
5. Connect a scan tool to the data link connector (DLC).
6. Monitor the idle speed on the scan tool.

Is the idle speed within the specified value?

700-800 RPM

Go to Step 3

Go to Step 4

3 | Observe the IAC Duty Cycle parameter on the scan tool. Is the IAC Duty Cycle parameter within the specified value? | 8-25% (8-35% at altitudes above 6,560 ft) | Go to Step 6 | Go to Diagnostic Aids

4

1. Inspect the lead wires and the hoses of the fuel injection system and of the EVAP control system for secure connections.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 6

Go to Step 5

5

1. Check the accelerator control cable for the correct movement and for any free-play.
2. Adjust as necessary. Refer to Accelerator Cable Adjustment .

Was an accelerator control cable adjustment necessary?

--

Go to Step 6

Go to Rough, Unstable, or Incorrect Idle and Stalling

6

1. Turn ON the A/C.
2. Monitor the idle speed on the scan tool.

Is the idle speed within the specified value?

825-925 RPM

Go to Step 7

Go to Air Conditioning (A/C) Idle Circuit Diagnosis

7 | Reevaluate the customer concern. Operate the vehicle at the speed and the conditions that duplicate the concern. Is the engine's performance at idle speed within acceptable limits? | -- | System OK | Go to Rough, Unstable, or Incorrect Idle and Stalling