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rough idle but steady rpms

Discussion in '80-Series Tech' started by AZcruiser, Dec 18, 2003.

  1. AZcruiser

    AZcruiser

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    As described the 94 runs great. But when engine is warmed up and set the truck vibrates at stop. The idle is steady around 500-600 rpms but I can feel and hear the idle through loose change etc. Of course the mirror rattles every once in a while.
    Possiblility of engine mount(s) going bad or even center bearing? The last tune up was about 1.5 years and I drive about 8k miles yearly. I realize the more its offroad more rattles will be heard but for 120k its not bad....more less a fine tune question.
    Chris
     
  2. cruiserman

    cruiserman

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    Does it rattle out of gear? I would check motor mounts, exhaust mounts, etc.
     
  3. Beowulf

    Beowulf

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    >> ... truck vibrates at stop. <<

    Chris,
    Can you isolate what is vibrating? Exhaust? Engine? Xfer case shifter?

    Without more information, identifying the cause will be a shot in the dark. It could be as simple as needing a minor tune (plugs or wires) or fuel system cleaner or something more complex like the wiring harness by the EGR or the big intake hose. Or, it could be something expensive like ... (you don't want to know.)

    -B-
     
  4. AZcruiser

    AZcruiser

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    The vibration goes away when I shift into neutral waiting for a light,etc. So this narrows to transmission to transfer case.
     
  5. wob

    wob

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    I went through something similar not too longf ago. It would shimmy a little in drive. After a while, it got worse, then as soon as you put it drive it would want to cut off. Neutral and Reverse worked fine. The culprit? Pinched harness by the engine. In reverse, the engine torqued the opposite way, so nothing happened. As soon as the engine torqued the other way, it would die. You may be at the early stages of what I had. HTH


    will
     
  6. wob

    wob

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    The main question is, does it do it in reverse? If not, I would suggest a bad wire or loose harness.
     
  7. wob

    wob

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    I guess I should have just edited my previous post instead of start a new one.
     
  8. Eduardo96FZJ80

    Eduardo96FZJ80

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    Wob,
    The last guy who posted three times in a row got got blasted by the Wulf :D

    Also, kinda curious as to which harness was getting "pinched" ?
     
  9. AZcruiser

    AZcruiser

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    In all drives it vibrates, its fighting against the brakes. Once off the brakes appears to be ok.
     
  10. wob

    wob

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    [quote author=Eduardo96FZJ80 link=board=2;threadid=8936;start=msg77980#msg77980 date=1071869807]
    Wob,
    The last guy who posted three times in a row got got blasted by the Wulf :D

    Also, kinda curious as to which harness was getting "pinched" ?
    [/quote]


    I'm curious too about which wire was getting pinched. I never saw.:doh: It was at my trusty mechanic's. He diagnosed it, so I never saw exactly where it was. He said it was behind the engine.

    BTW, I'm not scared of the big bad Wulf. :flipoff2: :flipoff2: :flipoff2:
     
  11. wob

    wob

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    Do these things have brake boosters? I think I had that problem once in my 40. Leaky brake booster made the engine rev funny when depressed. Something about loosing vacuum? Sound familiar? Anyone? Anyone? Bueller....
     
  12. Lars

    Lars

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    [quote author=wob link=board=2;threadid=8936;start=msg77994#msg77994 date=1071871510]
    Do these things have brake boosters? I think I had that problem once in my 40. Leaky brake booster made the engine rev funny when depressed. Something about loosing vacuum? Sound familiar? Anyone? Anyone? Bueller....
    [/quote]


    My 93 80 does that right now. It's new to me so who knows what leaks and what is broken. At least during warm-up and in nuetral, when I press the brakes there is a small surge in rpm's
     
  13. PHAEDRUS

    PHAEDRUS

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    I wouldnt rule out exhaust just yet. when you are in drive the engine is at a different pitch in the motor mounts and can make the exhaust rattle funny. I would chekc there first as it is a lot easier to repair a heat sheild than a trans.
    Dave
     
  14. AZcruiser

    AZcruiser

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    Dave, good point. I just remembered that the heat shield bolts came off a few months ago...the flange part that mounts to the chassis. A loose bolt was rattling than noticed it completely came off. I think thia flange part is threaded too. I doubt that is the main solution but a good starting point.

    Chris
     
  15. cruiserman

    cruiserman

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    [quote author=Lars link=board=2;threadid=8936;start=msg77998#msg77998 date=1071871706]
    My 93 80 does that right now. It's new to me so who knows what leaks and what is broken. At least during warm-up and in nuetral, when I press the brakes there is a small surge in rpm's
    [/quote]

    Normal.
     
  16. Lars

    Lars

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    [quote author=cruiserman link=board=2;threadid=8936;start=msg78066#msg78066 date=1071879045]
    Normal.
    [/quote]

    Thanks.