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2G IAC

Posted by AustinChristiansen, Sep 21, 2019

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  1. AustinChristiansen

    AustinChristiansen Probationary Member

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    Birch Run, Michigan
    So i had a rough idle when the car heated up to normal temp, whenever it idled for about 2 minutes or so it would fluctuate in rpms dropping to near stalling rpms (you can hear it) to about 1000 then settle at 700 again. so today i took out my iac and cleaned it all up it was extremely dirty. Then i plug it in to test if it worked which is vibrated which i heard is how you see if they work or not, so i was ready to go i plugged it in bolted it and i go to start the car after letting the ECU get familiarized after resetting the battery. it cranked but died out i tried again same result. i gave it gas but and it will run but as soon as you let go of the throttle it dies. please help guys i’m really in a slump i’ve tried numerous things to do to no avail.
     
  2. jpmxrider489

    jpmxrider489 Supporting VIP

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    Did you measure it with a volt meter. It should be 30ohm or 40 depending if you have a tan or black top. This is at a cold start? You have the fiav?
     

    2K  3

    1995 Eagle Talon TSi
    manual · 2G DSM
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  3. rabenne

    rabenne Proven Member

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    I think its suppose to actually move in and out (or out then in, I dont remember) not just vibrate. I believe I had one vibrate during that test when one of the wires for the IAC was damaged.

    the rolling idle could have been an idle switch problem. Do you have datalogging capability?
     

    Street Build 7K  8

    1995 Eagle Talon TSi
    awd · manual · 2G DSM
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  4. Bo0sTeD 4G63

    Bo0sTeD 4G63 Supporting Member

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    Miami, Florida
    Test the IAC first and verify it's working properly, if not see if you have a friend with one and swap it out.
     

    Street Build 951  1

    1997 Mitsubishi Eclipse GSX
    awd · automatic · 2G DSM
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  5. Vegas smith

    Vegas smith Proven Member

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    Houston, Texas

    Street Build 3K  10

    1993 Eagle Talon TSi AWD
    awd · manual · 1G DSM
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  6. AustinChristiansen

    AustinChristiansen Probationary Member

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    Joined Jul 27, 2019
    Birch Run, Michigan
    I ordered a new IAC and will be in tomorrow.. if i take the IAC out and crank it the car goes and revs high so i shut it off so it won’t redline. i put it back in this morning and it started up and i drove it a bit around my neighborhood (just fine) and parked it and shut it off and it would crank but not start again unless i revved it and it stayed alive then it stalled out every time i let go of the gas while driving.
     
  7. rabenne

    rabenne Proven Member

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    Okay it could be a bad IAC, but it could be the wiring going to it from the ecu. I had one bad wire and my IAC would only vibrate. Thats because not all of the coils are activating to create rotation motion. If its vibrating there is probably power and ground going to it, but one of the coil wires may have issues.

    I highly recommend you try wiggling around the harness and wires going to IAC while yo have someone else try to start the car and get it to idle. If it starts working again you have a wire issue in there. If it doesn't make any difference, I would still probably check the wires by removing the looming for a couple feet to visually see if there are any wire issues. OR you could throw a multi meter on each end of that wire (one at ECU, one at IAC) and wiggle the harness and watch for a change in resistance. you would have to do it for each of the coil wires.

    IF you have a wiring issue your new shiny IAC wont help, but it could be the IAC.

    Typically its best to diagnose stuff rather than parts swapping, but hell, you will have one now, so just throw that on and see if it fixes it...
     

    Street Build 7K  8

    1995 Eagle Talon TSi
    awd · manual · 2G DSM
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  8. AustinChristiansen

    AustinChristiansen Probationary Member

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    Birch Run, Michigan
    Well my car started and ran fine until it got heated up then it idled bad. other than that it had no problems but i was tired of the idle problem so i took it out and cleaned it and all of this occurred.

    Also, when i took the IAC out it was extremely dirty and caked with it on there. So i figured that was the problem but tomorrow after work i’ll inspect it like you’ve said and obviously test the new IAC
     
    Last edited by a moderator: Sep 23, 2019
  9. rabenne

    rabenne Proven Member

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    I think you are on track to solve the problem,

    Best of luck!

    Let us know what you find!
     

    Street Build 7K  8

    1995 Eagle Talon TSi
    awd · manual · 2G DSM
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  10. chrysler kid

    chrysler kid Proven Member

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    There is a proper process to run at warm idle to set idle for the idle air control valve at position 30 to set at 750-850 rpms. Anything out of this range would trigger a check engine light
     

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    1998 Mitsubishi Eclipse GST
    fwd · automatic · 2G DSM

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    fwd · manual · 2G DSM

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  11. tk106

    tk106 Supporting Member

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    Cincinnati, Ohio
    Pretty sure it won’t cause a cel when it’s out of range.

     

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    2000 Jeep Cherokee Sport - Classic
    awd · automatic · Misc Vehicles

    119  4

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    fwd · manual · Misc Vehicles

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    1992 Eagle Talon TSi AWD
    12.625 @ 111.42 · 1G DSM
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  12. AustinChristiansen

    AustinChristiansen Probationary Member

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    Joined Jul 27, 2019
    Birch Run, Michigan
    Thank you to everyone who helped! she is now running better than ever it was the IAC after all.
     
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  13. chrysler kid

    chrysler kid Proven Member

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    Mckinney, Texas
    For the 2g according to the factory service manual and my own experience rebuilding the throttle bodies, at position 30 the car at operating temperature needs to idle at its predetermined rpm range or the ecu will trigger code for the idle air control valve.

    To recalibrate the throttle body to set the base idle you must adjust the throttle stop screw and the biss screw. The biss screw determines how much air is let in by the iacv and determines idle at position 30 of the iacv based on the throttle body stop screw position

    If you ever have to do the throttle body recalibration procedure its like setting base idle on a carburetor except the throttle stop screw will destroy your hand when you try to adjust it, and you need a long obd2 cable to read your idle as you calibrate.

    There is a blue jumper harness behind the throttle body on the firewall to trigger position 30 on the idle air control valve.

    Long story short buy a rebuilt throttle body from a reputable vendor. It sucked to rebuild mine, I went through 3 of them. Probably the hardest process to understand on a dsm unless you understand the error code process flow in the factory service manual.

    Glad it was simple and just the iacv. I bought 3 of them close out on rock auto for $12 in addition to the 2 used ones I already have.

    More useless unfo: socketed ecus have problems with the grey idle air control valves. The stepper motors are stronger and can burn the sockets. The black iacv will use less power and better for older cars. If you have a 98-99 black box ecu the two piece design grey iacv is a nice piece, the stepper motor is more responsive to commands and I could tell the car would click through the progressions evenly kicking down the idle. The black units are more gradual and even, but the old school ones with a black box ecu were easier to calibrate and tell when they were at which position
     
    Last edited: Sep 23, 2019

    2K  15

    1998 Mitsubishi Eclipse GST
    fwd · automatic · 2G DSM

    2K  12

    1996 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM

    1K  0

    1996 Mitsubishi Eclipse GST
    14.1 @ 97 · 2G DSM
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