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Home >> Chevrolet >> 2005 >> Aveo Base, 4D Hatchback >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - 1.6L (L91) - Troubleshooting & Diagnosis >> Troubleshooting >> Idle Air Control (IAC) System Diagnosis >> Diagnostic Aids

Diagnostic Aids

Idle Air Control (IAC) System Diagnosis

Step Action Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check - Engine Controls? Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
IMPORTANT: Ensure that the Engine Speed parameter stabilizes with each Commanded RPM change to determine if the engine speed stays within 100 RPM below the commanded RPM or within 200 RPM above the commanded RPM.
  1. Start the engine.
  2. Turn OFF all accessories.
  3. Slowly increment the engine speed to 1,800 RPM, then to 600 RPM, then to 1,800 RPM with a scan tool.
  4. Exit the RPM Control function.
Is the engine speed within 100 RPM below the commanded engine speed or within 200 RPM above the commanded engine speed?		 Go to Diagnostic Aids Go to Step 3 
3
  1. Turn OFF the ignition.
  2. Disconnect the IAC valve.
  3. Connect the J 37027-1A  IAC Motor Driver to the IAC valve.
  4. Start the engine.
  5. Command the IAC valve in until 600 RPM is reached with the J 37027-1A  .
  6. Command the IAC valve out until 1,800 RPM is reached with the J 37027-1A  .
  7. Return the engine speed to the Desired Idle Speed parameter.
Did the Engine Speed parameter steadily decrease to 600 RPM and steadily increase to 1,700 RPM when the IAC valve was commanded in and out?		 Go to Step 5  Go to Step 4 
4 Did you observe an excessively high idle condition that could not be controlled with the IAC motor driver? Go to Step 11  Go to Step 12 
5
  1. Connect a test lamp between one of the IAC valve control circuits and a good ground.
  2. Start the engine.
  3. Observe the IAC Counts parameter with a scan tool.
  4. Command high RPM with the J 37027-1A  until the IAC Counts parameter starts to increment.
  5. Command low RPM with the J 37027-1A  until the IAC Counts parameter starts to increment.
  6. Return the Engine Speed to the Desired Idle Speed parameter.
  7. Repeat the above procedure for the other three IAC valve control circuits.
Did the test lamp remain ON, never flashing, while the IAC Counts were incrementing for any of the IAC valve control circuits?		 Go to Step 9  Go to Step 6 
6 Did the test lamp remain OFF and never flash while the IAC Counts were incrementing at any of the IAC valve control circuits during the above test? Go to Step 8  Go to Step 7 
7
  1. Connect a test lamp between the IAC coil A low control circuit and the IAC coil A high control circuit.
  2. Observe the IAC Counts parameter with a scan tool and the test lamp.
  3. Command high RPM with the J 37027-1A  until the IAC Counts parameter starts to increment.
  4. Command low RPM with the J 37027-1A  until the IAC Counts parameter starts to increment.
  5. Return the Engine Speed parameter to the Desired Idle Speed parameter.
  6. Repeat the above procedure with the test lamp connected between the IAC coil B low control circuit and the IAC coil B high control circuit.
Did the test lamp stay illuminated and never flash while the IAC Counts were incrementing during the above test?		 Go to Diagnostic Aids Go to Step 16 
8 Test the IAC valve control circuit where the test lamp remained OFF for the following:
  • An open
  • A short to ground
  • A short to another IAC valve control circuit

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 12 
9 Test the IAC valve control circuit where the test lamp remained illuminated for a short to voltage or a short to another IAC valve control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 14 
10
  1. Remove the IAC valve. Refer to Idle Air Control (IAC) Valve Replacement .
  2. Inspect for the following conditions:
    • The throttle body for damage and/or tampering
    • For vacuum leaks
    • For an incorrectly installed PCV valve and hose, if equipped
    • For a malfunctioning PCV valve
    • The throttle shaft for binding
    • The throttle linkage or cruise control linkage for binding
    • A skewed TP sensor signal
Did you find and correct the condition?		 Go to Step 17  Go to Step 13 
11
  1. Remove the IAC valve. Refer to Idle Air Control (IAC) Valve Replacement .
  2. Inspect for the following conditions:
    • The throttle body for damage and/or tampering
    • For excessive deposits on the throttle plate
    • For excessive deposits in the throttle bore
    • For debris in the IAC passage
    • For excessive deposits on the IAC valve pintle
    • For a restricted air intake system
Did you find and correct the condition?		 Go to Step 17  Go to Step 13 
12
  1. Disconnect the ECM.
  2. Test each IAC valve control circuit for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 14 
13 Test for an intermittent and for a poor connection at the IAC valve. 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 17  Go to Step 15 
14 Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 17  Go to Step 16 
15
IMPORTANT: If the IAC valve is removed or replaced, perform the Idle Learn Procedure.
Replace the IAC valve. Refer to Idle Air Control (IAC) Valve Replacement .Did you complete the replacement?		 Go to Step 17  -
16
IMPORTANT: If the ECM valve is removed or replaced, perform the Idle Learn Procedure.
Replace the ECM. Refer to Engine Control Module (ECM) Replacement .Did you complete the replacement?		 Go to Step 17  -
17
  1. Reassemble the vehicle as necessary.
  2. Clear any DTCs with a scan tool.
  3. Start the engine.
  4. Operate the system to verify the repair.
Did you correct the condition?		 Go to Step 18  Go to Step 2 
18 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 Go to Diagnostic Trouble Code (DTC) List System OK
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