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Thread: Bad ECU vs. Bad IAC Valve

  1. #1
    THING1JZ & THING2JZ
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    Default Bad ECU vs. Bad IAC Valve

    I'm trying to decide if this is a bad ECU or if my IAC valve is dying. If anyone has had experience with this I would appreciate any input. I replied to another thread but I figured if I posted here I might double my chances.

    Here's a few videos:








    These are all three different occasions and It works fine for a week or two in between.

    1989 White Package Supra 1JZGTE - THING1JZ
    1991 White Package Supra 2JZGTE - THING2JZ
    1976 Celica GT Liftback w/ built 20R/22R
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    Default Re: Bad ECU vs. Bad IAC Valve

    I'd say check the usual suspects concerning the ignition... i.e., cracked boots, bad wiring, bad grounds, etc. To eliminate the ISCV as a potential problem, unplug it and see how it runs. IIRC, it will start, rev up on its own, settle back down, rev up, and so on, until it is plugged back in.

    With mine, used to have to start it with the ISCV unplugged, then plug it in once the car was running, and that solved the issue for the most part. Yours however, I suspect you might have more than one issue here...
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  3. #3
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    Default Re: Bad ECU vs. Bad IAC Valve

    1J or 2j? You can also bench test it.
    http://wilbo666.pbworks.com/w/page/4...WireISCVWiring
    Also clean it real good while it's out.

    If it's a 1j open the ecu up and check the capacitors. If they are bad you'll see black goo around the capacitors.

  4. #4
    Dang Dude! No Way Man.
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    Default Re: Bad ECU vs. Bad IAC Valve

    My car did something similar but not nearly as bad. Rev up and down from 1k to 1500 like a bad tps or something. But it goes away when hot. Started last week and not all the time. Kinda cuts out too. Havnt looked into it.

  5. #5
    THING1JZ & THING2JZ
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    Default Re: Bad ECU vs. Bad IAC Valve

    Quote Originally Posted by S.A. supra View Post
    1J or 2j? You can also bench test it.
    http://wilbo666.pbworks.com/w/page/4...WireISCVWiring
    Also clean it real good while it's out.

    If it's a 1j open the ecu up and check the capacitors. If they are bad you'll see black goo around the capacitors.
    It is a 1J, I pulled the ECU out yesterday afternoon. It does have burnt spot, but was around 2 resistors rather than a capacitor. I'm going to send it off sometime this week. This problem has been happening long enough for me to replace all 6 coil packs and plugs, replaced the starter because sometimes it wouldn't start, and removed the turbo timer because I thought that might have been screwing with thing because it fried it self. I'll try test it in a few minutes and get back to you.

    Thanks, Jordan

    1989 White Package Supra 1JZGTE - THING1JZ
    1991 White Package Supra 2JZGTE - THING2JZ
    1976 Celica GT Liftback w/ built 20R/22R
    1985 Chevy Silverado w/ fully built SB350

  6. #6

    Default Re: Bad ECU vs. Bad IAC Valve

    I'd say it's your ecu or another issue. If you have a bad ISCV, your car would most likely idle at only one speed; either about 500, 900, 1400, or 3000rpm because it gets stuck in one of those positions. I tried out a few of them on my car. You can tell if it's shot by the bench test and also if the bearings don't spin smoothly (by comparing it to a good one). I actually figured out how to get them apart to fix them, but you can't get a replacement stepper motor or even disassemble it to rebuild it.

    In my case it was the ecu that seems to have gotten messed up in the ISCV logic. I can't say I've had that happen to me, but your ecu seems to have a capacitor problem from what I've heard others describe.

  7. #7
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    Default Re: Bad ECU vs. Bad IAC Valve

    Did you ever get this fixed? I am having the same issue now and it got so bad it barely idles and dies now. I pulled my ecu apart and saw that I had one small capacitor that was leaking.

  8. #8
    kanji
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    Default Re: Bad ECU vs. Bad IAC Valve

    It only takes one! I would suggest getting them all done since it is out and being fixed. Also, with the starter it might not be a bad idea to install an additional relay inline with the signal wire. Sometimes the clicking of the started can be the resistance in the wire itself.

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