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rough idle & no acceleration 700 1992

posted by  skowsa on  Fri Mar 28 18:37 CST 2003
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my '92 745t is still experiencing a really rough idle, it's almost like a put-put-put-put, in fact if I put my hand a few inches away from the tailpipe it sounds more like a big heavy helicopter in the distance.
Car has absolutely no acceleration either. Spark plugs are black but not wet. Fluids are full, timing belt was just replaced about 30 minutes ago and all marks lined up before and after, anyone have any suggestions?

thanks
Ian








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    rough idle & no acceleration 700 1992

    posted by  the kick inside on  Sun Mar 30 12:18 CST 2003
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    last visit: Thu May 17 09:58 CST 2007
    [RELATED]

    you say plugs are black..as in tan toloured electrodes or black, they should be tan - chuck a set of plugs at it anyway, nothing fancy just a new set properly gapped...could just be a bad plug...








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    rough idle & no acceleration 700 1992

    posted by  Aye Roll on  Fri Mar 28 19:21 CST 2003
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    last visit: Tue Oct 14 21:08 CST 2014
    [RELATED]

    Yeah, you've got a big vacuum leak probably caused by a hole in one of the big black rubber hoses that go to the turbo outlet, intercooler, or intake manifold. Oil in the airstream, from the crankcase vents or the turbo seals, eats away at the rubber hoses from the inside. Pull them off and replace any that are rotten. (Of course, your Homeland Security duct tape will make a very effective temporary patch until you can get a new hose.)
    --
    Rob Bareiss, New London CT ::: "Roterande Fläkt Och Drivremmar!"








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      rough idle & no acceleration 700 1992

      posted by  skowsa on  Sat Mar 29 01:48 CST 2003
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      I've searched those hoses and not found a thing, they look to be in pretty good condition.

      Ian








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        rough idle & no acceleration 700 1992

        posted by  david hunter on  Sat Mar 29 04:11 CST 2003
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        last visit: Mon Jun 30 22:10 CST 2014
        [RELATED]

        How many cylinders are you running on, If less than 4, have you isolated the cylinder by pulling off plug wires one at a time?

        Are plugs, wires, rotor, cap all in good shape.

        Be carefull about proceeding to just change parts, better to diagnose the problem. The timing belt would not typically cause the problem you described. If you make an error installing something you then have 2 problems and it goes downhill from there.
        --
        David Hunter








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          rough idle & no acceleration 700 1992

          posted by  skowsa on  Sat Mar 29 05:17 CST 2003
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          after posting the symptoms here and on al.autos.volvo it was suggested that the timing belt could have slipped a tooth and that's why I checked/replaced that. I am no diagnostic expert so I was going by what more than one person suggested.
          Don't worry, I have no intention of just replacing parts - don't want to throw my money away.
          Cap & rotor aren't even a year old, I just took them off and they look fine - a little worn, but nothing outrageous looking. Don't know about wires they're Volvo bougicord (sp?) I kinda flexed and jiggled them all while the engine was running and noticed no difference.
          Also disconnected Oxygen sensor and noticed no difference.

          How would I know if I'm not running on all 4 cylinders?
          Can I just pull the spark plug wires off the plugs while the engine is running?

          thanks
          Ian








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            rough idle & no acceleration 700 1992

            posted by  david hunter on  Sat Mar 29 11:50 CST 2003
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            last visit: Mon Jun 30 22:10 CST 2014
            [RELATED]

            The description you gave may indicate an engine just running on 3. To confirm or deny, the procedure is to run the engine with each plug wire off one at a time. Remove and replace the wires with engine off. If a cylinder is not firing you will know because removal of that wire will make no difference in the idle or power. It's just a quick test.
            If you are firing on all 4 then proceed to other things, you can do similar test of course with the injectors.
            What is your idle RPM? Check engine light on, any fault codes?
            --
            David Hunter







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