Idle Air Control (IAC) System Check

Idle Air Control (IAC) System Check










Troubleshooting

1. Engine idle speed and IAC duty check

Check idle speed / idle air control duty referring to Adjustments Idle Speed / Idle Air Control (IAC) Duty Inspection and Adjustment.

Is check result as specified?
YES
Go to Step 2.
NO
Go to Step 4.

2. Idle air control valve check

Turn headlight, heater blower and/or rear defogger ON.

Is idle speed kept specified speed?
YES
Go to Step 3.
NO
Go to Step 5.

3.
Is engine idle speed kept specified speed even with steering wheel turned to the right or left as far as it stops (vehicle with power steering system)?
YES
System is in good condition.
NO
Check power steering pressure switch signal circuit referring to Testing and Inspection Power Steering Pressure (PSP) Switch Signal Circuit Check.
If check result is OK, go to Step 5.

4. Air intake system check

Check air intake system for clog and air inhaling.
Check fast idle plunger length referring to Fast Idle Control System On-Vehicle Inspection Fast Idle Control System On-Vehicle Inspection.

Are the check result satisfactory?
YES
Go to Step 5.
NO
Repair or replace.

5. Idle air control valve operation check

Check idle air control valve for operation referring to P0505 DTC P0505 / P0506 / P0507: Idle Air Control (IAC) System Malfunction / RPM Lower than Expected / RPM Higher than Expected.

Is check result satisfactory?
YES
Go to Step 7.
NO
Go to Step 6.

6. Idle Air Control Valve Check

Check idle air control valve for resistance and operation referring to P0505 DTC P0505 / P0506 / P0507: Idle Air Control (IAC) System Malfunction / RPM Lower than Expected / RPM Higher than Expected.

Is check result as specified?
YES
"BLK/RED" or "GRN/RED" circuit open or short.
If wire and connections are OK, substitute a known-good ECM and recheck.
NO
Clean or replace, idle air control valve.

7. Air conditioning (A/C) signal check

Check A/C signal circuits referring to A/C Signal Circuits Check (Vehicle with A/C) A/C Signal Circuits Check (Vehicle with A/C)
, if equipped.

Is it in good condition?
YES
Go to Step 8.
NO
Repair or replace A/C signal circuits or A/C system.

8. Check parts or system which can effect idle speed / IAC duty:

Check the accessory engine road
Check the EGR valve malfunction (leakage)
Check the EVAP system malfunction (leakage)
Check the Engine mechanical (Compression)
Check the TP sensor performance
Check the ECT sensor performance
Check the stuck of PCV valve

Are they in good condition?
YES
Go to Step 9.
NO
Repair or replace.

9. Idle air adjusting screw check

Adjust idle speed and idle air control duty referring to Adjustments Idle Speed / Idle Air Control (IAC) Duty Inspection and Adjustment.

Are specified idle speed and idle air control duty obtained?
YES
Idle air adjusting screw maladjusted.
NO
Clog of idle air passage.
If OK, substitute a known-good ECM and recheck.