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Thread: Vacuum leak idle hunting

  1. #1
    Senior Member
    Join Date:  May 2011

    Location:  New Jersey

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    Vacuum leak idle hunting

    I had to remove the fuel distributor because the sliding valve inside was gummed up. I replaced all the copper washers. When I put everything back together the car hunts idle.
    Yes I can take it apart again and replace the washers again but I was wondering if there was a easier way to diagnose the leak causing the idle to hunt high and low. It might not even be the FD maybe I disturbed something else. I do not own a fogging machine. Will spraying starter fluid around help? Thanks in advance......

  2. #2
    Senior Member
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    Location:  San Diego, CA

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    My VIN:    10353

    Maybe try to jump the RPM relay first to see if you have an obvious fuel line leak. Might be better to do that first before spraying more flammable fluid around.

    When I just replaced a bunch of fuel lines and VOD stuff after first starting it hunted for a while. Then after a long drive it seemed to clean everything out and now idles normally. You might also try taking it for a nice drive too (after making sure the fuel lines aren't leaking of course! )

  3. #3
    Senior Member
    Join Date:  May 2011

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    I will jump the rpm relay. Is the procedure jumping the relay without the car running and look around for leaking fuel in the engine compartment?
    I just remembered I do have a Party
    Fogging machine. Not sure if that will work as a smoker....

  4. #4
    Senior Member
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    Ya, the pump will run without the car on. Easy to spot and/or hear a leak. I had my battery terminal ready for a quick disconnect in case fuel started spraying in the back.

    The smoke machine might work if it's like the same mineral oil. I've also heard of using a cigar and extra bit of hose!

  5. #5
    Senior Member
    Join Date:  May 2011

    Location:  New Jersey

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    Thank you for your help! Do you think if itís the copper gasket under the fuel distributor leaking fuel would show up there?
    Is the smoke fluid for the party fog machine safe to use in the car?

  6. #6
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    My VIN:    03572

    The most common causes of idle hunting are a weak O2 sensor and or a dirty idle motor. But some cars seem to hunt a little no matter what you do. Also the adjustment of the curb idle screw will change the position of the idle motor opening so sometimes that also helps.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
    Senior Member
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    Location:  New Jersey

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    I just canít remember if it idle hunted before I took the Fuel distributor apart. So I was thinking that was the vacuum leak causing the problem. I will clean the idle motor. What do you recommend to do that? After that I will adjust curb idle. Is the fogging/smoke machine I have a good idea?

  8. #8
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    7,374

    My VIN:    03572

    Quote Originally Posted by coreydmc View Post
    I just canít remember if it idle hunted before I took the Fuel distributor apart. So I was thinking that was the vacuum leak causing the problem. I will clean the idle motor. What do you recommend to do that? After that I will adjust curb idle. Is the fogging/smoke machine I have a good idea?
    Use a solvent to clean the valve in the idle motor. Shake or blow out the solvent, let it dry and use a little light oil on the valve. Don't turn the valve with anything metal, use wood so you don't scratch it.

    You won't hurt anything using party smoke machine. I was planning on putting a smoke bomb in a jar with a hose to test but never tried it.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
    Senior Member
    Join Date:  May 2011

    Location:  New Jersey

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    I jumped the rpm relay looking for fuel
    leaks everything seems good Then, I cleaned the idle control valve with carb cleaner. It was gummed up. I filled it up and plugged both ends shook it around poured the dirty carb cleaner out and repeated until carb cleaner was clear, poured a few dropped of oil in it. Now moves freely. I also reset my curb idle screw and micro switch screw.
    I backed both screws out all the way. Tightened the idle until the idle arm just started to move plus 1/2 turn. Then I adjusted the micro switch screw until I heard it click and added a full turn. My idle is now much better.
    Now I have a exhaust leak on the drivers side. Hard to tell if itís the crossover pipe, cat, or exhaust manifold. Is there a trick to tell where itís leaking?
    Thanks for all your help!

  10. #10
    Delorean Guru
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    If it exhaust is leaking it is most likely the gasket. Just do them both. You should order a stud kit too.
    David Teitelbaum

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