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Thread: '86 Fiero GT idiols high

  1. #1

    '86 Fiero GT idiols high

    I just got an 1986 Fireo GT, I noticed that is idiol's to high around 2500 rpm. Does anyone know what this might be? I haven't check the trouble codes yet.
    www.xvelocity.com

  2. #2
    Senior Member
    Join Date
    Dec 2001
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    417

    Re: '86 Fiero GT idiols high

    Hey William:
    * * *Sounds like some compression loss somewhere.

  3. #3
    Senior Member
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    Re: '86 Fiero GT idiols high

    William: My car does the same thing... have to check all vaccum hoses and EGR stuff...

    "vacuum leak is the most common cause of a high idle. follow the egr tube up to the plenium and look at it carefully - use a mirror and flashlight if you have to.
    If you cant see any crack look for black areas in one of the rippled bands - black indicates an exhaust leak when the erg is open = vacuum leak the rest of the time.

    Another way is to spray wd40 where you think there might be a vacuum leak with the engine running - if you spray a leak it will alter the idle - slows it down I think.

    use a dental mirror and flashlite and follow each vacuum line across the engine end to end and make sure they are all attached - do the wd40 thing as much as you can."


    "he EGR valve sits on the exhaust crossover pipe near the coil. There is a tube that is bolted between the side of the EGR valve and the underside of the red upper intake plenum. The original tube is made of corrugated steel and is covered with an insulating blanket wrap. With age this tube developes cracks and allows air to be sucked into the intake manifold downstream of the throttle body. This is called un-metered air because the TPS (Throttle position sensor) does not know it is getting into the engine.

    The Oxygen sensor senses the lean exhaust due to the extra air and calls for more fuel from the injectors to keep the exhaust clean. Hence the raised idle speed.

    How do you check to see if the EGR tube is cracked? With the engine running at idle (wherever that may be in the current condition) wiggle the EGR tube to see if it has an effect on idle speed. You can also spray some WD-40 between the tube and its insulating blanket to see if it has an effect on idle speed. If it does then the tube is likely cracked.

    Replacing the tube is not all that hard to do but getting to the bolts underneath the plenum is a bit tight. I use a 1/4" ratchet with an extension to get them. The bolts are around 10mm or so.

    OEM replacement tubes are pretty expensive. Aftermarket ones aren't much cheaper but are usually better constructed. The tubes from older 2.8L engines from Pontiac 6000 and Camaros and Firebirds will fit if you elongate the holes in one of the flanges. They can be gotten from donor cars for 5 to 10 dollars.

    well sort of - after i pullled the intake plenium and fixed the creature damaged vacuum leak, brazed my egr tube, cleaned the intake butterfly with throttle body cleaner, and put it all back together the car ran great except for one thing:
    in neutal it was idleing at amost 2,000 rpm. In gear it was idleing ok, dropped right down to 900 rpm.

    I checked all over for vacuum leaks with the wd40, and found none. I thought maybe when I cleand the intake butterfly I had pushed some of the goopy carbon into the butterflys way, so it wasnt closing all the way.

    I found an interesting little screw next to the throttle cable cam, took a good look at it and sure enough, there is a screw that controls how far the buttterfly closes when the foot is off the gas pedal.

    I started the car up, let it get to temp, turned the screw and I could see the plate closing more and more, and the rmps started dropping - got it right down to 900 rpm at idle!

    I think maybe the previous owner had messed with it - dont think it should normally have to be adjusted for any reason - but in my case it fixed my high neutral-idle problem."

  4. #4

    Re: '86 Fiero GT idiols high

    Thanks Ari I'll check it out.
    www.xvelocity.com

  5. #5

    Re: '86 Fiero GT idiols high

    You Were right on the money Ari, the line from the EGR to the intake had a large crack in it...Thanks
    www.xvelocity.com

  6. #6
    Senior Member
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    Re: '86 Fiero GT idiols high

    Awesome Glad to Help someone!

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