Results 1 to 10 of 10

Thread: Setting IAC (Idle air control) valve

  1. #1
    Senior Member 85_Ciera_Rebuild's Avatar
    Join Date
    Sep 2007
    Location
    Kansas
    Posts
    5,282

    Default Setting IAC (Idle air control) valve

    I saw this video, and wonder about his words of "wisdom."

    If turning the ignition on causes IAC to engage plunger fully forward, then there is no purpose in doing what he is suggesting.

    Another person suggested, "The ECM “resets” the IAC valve when the car is operated at normal road speeds (35mph or more). During this time, the IAC valve is typically extended out all the way (IAC counts = 0), thus closing off the idle air passage. This helps the ECM “learn” the position of the IAC valve. Any time the IAC valve is replaced, this “learn” procedure should be performed."

    And, I found a limited tech overview here, which suggested, "When installing a new GM IAC or Chrysler AIS motor, the pintle must not extend more than a certain distance from the motor housing. The specs vary, so check the manual. Chrysler says one inch (24.50 mm) is the limit, while some GM allow up to 28 mm on some units and 32 mm on others. If the pintle is over extended, it can be retracted by either pushing it in (GM) or by connecting it to its wiring harness and using actuator test #03 to move it in (Chrysler).



  2. #2
    Senior Member AVTechMan's Avatar
    Join Date
    Aug 2011
    Location
    Grandville, MI
    Vehicle
    '87 Pontiac 6000 LE Wagon
    Posts
    585

    Default

    The IAC pintle going fully forward is true, as I had removed mine a few months ago to clean it up, and had turned the key on by accident, but my doing so the plunger went all the way forward which tells me that it moves forward when the key is in the On position.

    In most cases, and it can vary with different cars, when I had replaced the ECM in my wagon back in early August, I had to do the relearn procedure from scratch as when I started the car cold it died right away because there were no values stored. As I had it sitting and idling, I watched the RPM's change up and down during the course of 15 minutes, with the SES light coming on a few times and the idle went low enough to the point of almost stalling, but didn't go out. I believe the ECM was moving the IAC to different positions and making memory of it under differing idling conditions. After the time passed and I shut the car off, I started it and it fired up with no problem, as the ECM learned the position of the IAC.

    Idle adjustments on my car are not adjustable by hand, as it says on the Emission sticker on the strut tower, including timing adjustment (DIS coil packs) and idle.
    My A-Body Cars (past and present), meet the family:

    Car With No Name: 1984 Oldsmobile Cutlass Ciera w/Iron Duke (My first car, R.I.P.)
    Camilla: 1985 Chevy Celebrity Eurosport 2.8L V6 MPFI Iron Head (My new road cruiser)
    Jeanette: 1987 Pontiac 6000 LE Wagon 2.8L V6 (The daily driver)
    Danielle: 1984 Oldsmobile Cutlass Ciera 4.3L V6 Diesel (Finally getting overhauled)

  3. #3
    Senior Member 85_Ciera_Rebuild's Avatar
    Join Date
    Sep 2007
    Location
    Kansas
    Posts
    5,282

    Default

    Quote Originally Posted by AVTechMan View Post
    ECM...relearn procedure from scratch
    Reset ECM by pulling ECM fuse (underhood) for a few seconds.

    With A/C turned off, start car and immediately put it in Drive with your foot on the brake.

    If the car does not start initially, keep trying WITHOUT putting your foot on the accelerator.

    Idle the vehicle in Drive for autos and neutral for manuals until the coolant fan has cycled on then off for one minute.
    Shut off the car for 10 seconds.

    GM Engineering says to the above, "Step 3 states to Idle for 5 minutes. The software in the ECM NEEDS TO SEE THE COOLANT FAN CYCLE ON then OFF to LEARN the Base IAC position for the relearn. So the step should read: Idle the vehicle in Drive for autos and neutral for manuals until the coolant fan has cycled on then off for one minute. Then you may turn it off. (from GM 60 degree Engineering) "

  4. #4
    Senior Member 85_Ciera_Rebuild's Avatar
    Join Date
    Sep 2007
    Location
    Kansas
    Posts
    5,282

    Default

    Quote Originally Posted by AVTechMan View Post
    Idle adjustments on my car are not adjustable by hand
    Most likely, there is a throttle stop, but I would not mess with it.

  5. #5
    Senior Member AVTechMan's Avatar
    Join Date
    Aug 2011
    Location
    Grandville, MI
    Vehicle
    '87 Pontiac 6000 LE Wagon
    Posts
    585

    Default

    Yep, I have read that procedure. But its difficult to put the car in drive with foot on the brake if the engine stalls when you try to start it. There are several different procedures that I have read but the one I have done worked best for my car. To idle for five minutes isn't enough time because the coolant temp has to be about 230F before the cooling fan comes on. The idle drops slightly of course once it kicks on, which is what the ECM needs to see. It also verifies the CTS is doing its job as well.
    My A-Body Cars (past and present), meet the family:

    Car With No Name: 1984 Oldsmobile Cutlass Ciera w/Iron Duke (My first car, R.I.P.)
    Camilla: 1985 Chevy Celebrity Eurosport 2.8L V6 MPFI Iron Head (My new road cruiser)
    Jeanette: 1987 Pontiac 6000 LE Wagon 2.8L V6 (The daily driver)
    Danielle: 1984 Oldsmobile Cutlass Ciera 4.3L V6 Diesel (Finally getting overhauled)

  6. #6
    Senior Member AVTechMan's Avatar
    Join Date
    Aug 2011
    Location
    Grandville, MI
    Vehicle
    '87 Pontiac 6000 LE Wagon
    Posts
    585

    Default

    Quote Originally Posted by 85_Ciera_Rebuild View Post
    Most likely, there is a throttle stop, but I would not mess with it.
    Neither would I. Why seek a problem? That's why GM put a tamper-proof cap of some sort over that screw. The only time that may have to be messed with is if some major engine or intake changes are made that may effect the base idle.
    My A-Body Cars (past and present), meet the family:

    Car With No Name: 1984 Oldsmobile Cutlass Ciera w/Iron Duke (My first car, R.I.P.)
    Camilla: 1985 Chevy Celebrity Eurosport 2.8L V6 MPFI Iron Head (My new road cruiser)
    Jeanette: 1987 Pontiac 6000 LE Wagon 2.8L V6 (The daily driver)
    Danielle: 1984 Oldsmobile Cutlass Ciera 4.3L V6 Diesel (Finally getting overhauled)

  7. #7
    Senior Member 85_Ciera_Rebuild's Avatar
    Join Date
    Sep 2007
    Location
    Kansas
    Posts
    5,282

    Default

    Quote Originally Posted by AVTechMan View Post
    Yep, I have read that procedure.
    Diagnosing Intermittent Idle Speed Increases
    Group Ref.: Engine Fuel & Emission
    Bulletin No.: 476510
    Date: May, 1994

    INFORMATION

    SUBJECT:
    DIAGNOSING INTERMITTENT ENGINE IDLE RPM INCREASE

    MODELS:
    1988-89 BUICK CENTURY AND REGAL
    1988-89 CHEVROLET BERETTA/CORSICA, CAVALIER AND CELEBRITY
    1988-89 OLDSMOBILE CUTLASS CIERA AND SUPREME
    1988-89 PONTIAC GRAND PRIX AND 6000
    WITH 2.8L ENGINE (VIN W - RPO LB6)

    1989-93 BUICK REGAL
    1990 CHEVROLET CELEBRITY
    1990-92 CHEVROLET CAMARO
    1990-93 CHEVROLET BERETTA/CORSICA
    1990-94 CHEVROLET CAVALIER AND LUMINA
    1989-93 OLDSMOBILE CUTLASS SUPREME
    1989-91 PONTIAC 6000
    1989-93 PONTIAC GRAND PRIX
    1990-92 PONTIAC FIREBIRD
    1991-94 PONTIAC SUNBIRD
    WITH 3.1L ENGINE (VIN T - RPO LHO)

    1991-94 CHEVROLET LUMINA
    1991-94 OLDSMOBILE CUTLASS SUPREME
    1991-94 PONTIAC GRAND PRIX
    WITH 3.4L ENGINE (VIN X - RPO L01)

    1993-94 CHEVROLET CAMARO
    1993-94 PONTIAC FIREBIRD
    WITH 3.4L ENGINE (VIN S - RPO L32)

    1994 BUICK REGAL AND SKYLARK
    1994 CHEVROLET BERETTA/CORSICA
    1993-94 OLDSMOBILE CUTLASS SUPREME
    1994 OLDSMOBILE ACHIEVA
    1994 PONTIAC GRAND AM AND GRAND PRIX
    WITH 3.1L ENGINE (VIN M - RPO L82)

    The following information may assist in the diagnosis and correction of an intermittent increase in engine rpm with closed throttle (accelerator pedal not depressed). Typically there is no malfunction indicator light associated with the condition.

    The engine control system sensors are supplied a 5 volt reference signal to ensure properly scaled readings to the engine control module (ECM). If a large current draw flows through the circuit supplying the 5 volt reference, the input signals, as read by the ECM, will be skewed low. The ECM program will store an incorrectly low throttle position sensor signal as zero. If the reference voltage returns to normal, the ECM will interpret the resultant high throttle position sensor signal as an open throttle and idle air control steps (throttle follower) will be added accordingly, causing an increase in the engine rpm at idle.

    The A/C pressure transducer has been found to be especially vulnerable to shorts during the engine crank process. Electrical wires in the engine harness that are unprotected and rub on structural members also will cause the problem.

    Inspect all wiring and sensors associated with the 5 volt reference signal for shorts and correct as necessary.

    If the vehicle also has a condition associated with the air conditioning system, diagnose and correct as necessary.

    With a Techline Diagnostic Tool, read the throttle position sensor, manifold absolute pressure sensor, and A/C pressure transducer voltage with the key on-engine off.

    If all three voltage readings are skewed below their normal ranges, inspect the A/C pressure transducer.

    If all three voltage readings are within normal ranges, disconnect the battery for one (1) minute, reconnect and start the engine. If the increase in engine rpm at idle condition is gone, inspect the A/C pressure transducer.

    NOTE: On the LB6 (2.8L VIN W), LHO (3.1L VIN T) or L01 (3.4L DOHC VIN X) engines, If the ECM Is without battery power for any reason, then the Idle air control valve (IACV) position information for a stable satisfactory engine Idle Is "lost" and replaced with a default value. To correct the IACV position Information, perform an Idle relearn procedure using a Techline Diagnostic Tool. You can also manually relearn the Idle by following the procedure below.

    1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position.

    2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals.

    3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

    4. Turn the ignition key to the "off" position for at least 5 seconds.

    5. Repeat Step 2.

    6. Allow the engine to run for at least five (5) minutes.


    The correct IACV values for proper idle control will now be stored.

  8. #8
    Senior Member turbokinetic's Avatar
    Join Date
    Dec 2007
    Location
    Northport, AL
    Vehicle
    1984 Buick Century Olympia 3.8SFI Turbo V6
    Posts
    4,538

    Default

    Here is some more first-hand experience info on the IAC. I've had to actually program these values into ECM's on my project cars.

    IAC "parking" position:
    When the key is turned OFF, the ECM will move the IAC plunger to a "parking" position. This is used for startup of the engine. I beleive this is a complete sweep all the way out and back in.

    As soon as the key is turned on, the IAC will be moved to a startup position, based on coolant temperature.

    As soon as the engine is started, the IAC will move gradually, to a different position, based on coolant temperature. This is your cold-engine high-idle function.

    Finally, the ECM will begin using "closed-loop idle speed control" logic to control the IAC position and regulate the idle speed. The dynamics of this logic are learned based on the engine's idle performance. This is what you are teaching it with the Idle Learning procedure.

    When you drive off, the ECM will move the IAC to "reset" position (varies based on temperature). It is not closed all the way, it actually increases the idle to help prevent stalling. It stays at this fixed position until you come to a complete stop. Then it resumes idle speed regulation.

  9. #9
    Senior Member Century7667's Avatar
    Join Date
    Dec 2008
    Location
    Sugar Land, TX
    Vehicle
    1996 Buick Century Limited 3100 V6 / 1995 Buick Century Special 3100 V6 / 2001 Chevy S-10 LS 2.2L
    Posts
    1,967

    Default

    Quote Originally Posted by turbokinetic View Post
    Here is some more first-hand experience info on the IAC. I've had to actually program these values into ECM's on my project cars.

    IAC "parking" position:
    When the key is turned OFF, the ECM will move the IAC plunger to a "parking" position. This is used for startup of the engine. I beleive this is a complete sweep all the way out and back in.

    As soon as the key is turned on, the IAC will be moved to a startup position, based on coolant temperature.

    As soon as the engine is started, the IAC will move gradually, to a different position, based on coolant temperature. This is your cold-engine high-idle function.

    Finally, the ECM will begin using "closed-loop idle speed control" logic to control the IAC position and regulate the idle speed. The dynamics of this logic are learned based on the engine's idle performance. This is what you are teaching it with the Idle Learning procedure.

    When you drive off, the ECM will move the IAC to "reset" position (varies based on temperature). It is not closed all the way, it actually increases the idle to help prevent stalling. It stays at this fixed position until you come to a complete stop. Then it resumes idle speed regulation.
    Interesting. So, is this what is going on for my S-10 when I begin to let the clutch out? I noticed that the engine will comphensate when I load it, and also the increased idle when the A/C is running (presumably for cooling the condenser with the engine driven fan)?

    Thanks,
    Ken T.

  10. #10
    Senior Member 85_Ciera_Rebuild's Avatar
    Join Date
    Sep 2007
    Location
    Kansas
    Posts
    5,282

    Default

    1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position.

    2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals.

    3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

    4. Turn the ignition key to the "off" position for at least 5 seconds.

    5. Repeat Step 2.

    6. Allow the engine to run for at least five (5) minutes.


    The correct IACV values for proper idle control will now be stored.
    It works...just did it today

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •