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Idle Question

Discussion in '80-Series Tech' started by Underdog, May 20, 2003.

  1. Underdog

    Underdog

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    Hey all,

    My rig has a surging idle and I was wondering if it is normal.  It has been like this since I've owned it for the last 5 months.
    At first I thought maybe when the A/C kicked on the RPM increased but I think it does it regardless of whether the A/C is on or not.  Then I thought maybe there was a big alternator draw?

    The engine idles around 500 RPM and then it will surge up to 800-1,000 for a while and then go back down to 500.  It seems random - will do it at stop lights or when its in park and just sitting in the driveway.  It might stay at 800-1,000 for a minute or two and then go back down to 500.

    Any thoughts?
     
  2. Hltoppr

    Hltoppr SILVER Star

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    That seems like a little too much surge. The standard idle is set at 625 rpm, but I've seen 500 rpm while in Drive. There is some variation, but going up to the 800-1000 range seems excessive without the AC on. Has the vehicle thrown a code?

    -H-
     
  3. Underdog

    Underdog

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    No codes and it starts and runs fine. The idle isn't an issue either really, just wondered if it was normal or if this is a sympton of some big problem.
     
  4. Hltoppr

    Hltoppr SILVER Star

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    Like I said, that much fluctuation is interesting. Mine varies a little bit, but not like that.

    If it runs fine you might just check all of your vacuum lines for small leaks, try a tune up, etc.

    -H-
     
  5. CruisinGA

    CruisinGA

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    I know its not the same truck, but a good friend of mines F 150 fluctuates about the same range your's does, hes spent mucho money and time trying to figure it out, so far no go. Even the best local performance garage can't figure it out. (best according to him, I don't use any garage but my own.)
    So good luck, your gonna need it.
     
  6. Beowulf

    Beowulf

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    Randy,
    Have you addressed all the tune-up basics like plugs, wires, PCV valve, dizzy cap and rotor?

    If so, start looking at these things:
    1. Vacuum leak.
    2. Cracks on the underside of the big hose to the AF.
    3. Lube the throttle cables.
    4. Clean the injectors.
    5. Clean the throttle body.

    -B-
     
  7. cruiserdan

    cruiserdan SupportingVendor Emeritus Supporting Vendor Moderator

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    Check the throttle cable to make sure it "Returns to idle" .

    The cable should have a bit of slack in it at rest. I am seeing a few high mileage 1FZ's with worn out cables. This can also happen when a blower is added and the throttle body is rotated into position on the adapter without loosening the nuts and re-tightening after re-location.


    Dan :beer:
     
  8. Underdog

    Underdog

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    As a follow-up guys - I've paid attention to what is going on and we had a cool streak so I left the A/C off for a while.

    With the A/C off the idle never changes. With the A/C on it occasionally cycles up to a higher idle and then back down. Its not that dramatic a change and I think its normal as the compressor kicks in/out.
     
  9. Beowulf

    Beowulf

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    >> With the A/C on it occasionally cycles up <<
    >> to a higher idle and then back down. <<

    Normal.
    -B-