DTC 35

Code 35 - Idle Air Control (IAC) System:

Wiring Diagram For Code 35 - Idle Air Control (IAC) System:

CODE 35 - IDLE AIR CONTROL (IAC) SYSTEM


Circuit Description:

Code 35 will set when the closed throttle engine speed is 100 RPM above or below the correct engine idle speed for 45 seconds.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Continue with test even if engine will not idle. If idle is too low, "Scan" will display 80 or more counts, or steps. If idle is high, it will display "0" counts. Occasionally, an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up and down. Disconnect IAC. If the condition is unchanged, the IAC is not faulty, there is a system problem. Proceed to paragraph three below.

2. When the engine was stopped, the IAC valve retracted (more air) to a fixed "Park" position for increased air flow and idle speed during the next engine start. A "Scan" will display 100 or more counts.

3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.

4. There is a remote possibility that one of the circuits is shorted to voltage which would have been indicated by a steady light. Disconnect ECM and turn the ignition "ON" and probe terminals to check for this condition.

Diagnostic Aids:

A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. "Scan" counts will be above 60 counts if too low and "0" counts if too high.

If idle is too high, stop engine. Ignition "ON". Ground diagnostic terminal. Wait a few seconds for IAC to seat, then disconnect IAC. Start engine. If idle speed is above 800 +/- 50 RPM, locate and correct vacuum leak.



^ System Too Lean - (High Air/Fuel Ratio)
Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. May set Code 44. "Scan" and/or Voltmeter will read an oxygen sensor output less than 300 mv (.3 volts). Check for low regulated fuel pressure or water in fuel. A lean exhaust with an oxygen sensor output fixed above 800 mv (.8 volts) will be a contaminated sensor, usually silicone. This may also set a Code 45.
^ System Too Rich - (Low Air/Fuel Ratio)
Idle speed too low. "Scan" counts usually above 80. System obviously rich and may exhibit black smoke exhaust. "Scan" tool and/or voltmeter will read an oxygen sensor signal fixed above 800 mv (.8 volts).

Check:

- High fuel pressure
- Injector leaking or sticking.

^ Throttle body
Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging the bore.
^ A/C Compressor or Relay Failure
See Chart C-10. If the relay is faulty, an idle problem may exist.
^ Refer to "Rough, Unstable, Incorrect Idle or Stalling", see Diagnosis By Symptoms - No Trouble Codes Stored.