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motor won't run above 2000 rpm 900

posted by  calvic on  Fri Oct 15 14:05 CST 2004
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last visit: Tue Jul 6 10:01 CST 2010
[RELATED]

1994 940 w/ turbo.
Car was idling pretty bad and wouldn't accellerate. I replaced FPR and threw a set of plugs at it, now it idles good but It just refuses to run above 2k rpm. It stumbles and sound like a backfire thru the induction. I unpluged the AMM connector and the idle picked up and it sounded pretty good, but it wont take any throttle with it disconnected (is that how it works). prior to this the car ran great the day before, turned to crap setting in the garage overnite. Any thoughts?
Thanks
JJ








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    motor won't run above 2000 rpm 900

    uid 14317's pic
    posted by  Most Unusual on  Fri Oct 15 23:02 CST 2004
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    last visit: Tue Jan 7 20:53 CST 2014
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    Ready for this one...the air intake box has a foam liner (silencer) in the top of it. As it ages, it deteriorates and peels off, becoming trapped in the mass air sensor...choking the engine. It can also clog the inter-cooler, and/or pass through and enter the engine. If this is the problem, once cleaned out, the engine should run just fine. However, when you give it full throttle and release the pedal, you may hear a lot more air noise (turbulence) from the air box.

    I had a 1992 740 turbo...this happened to me. Took me a while to find the problem.

    One other possiblity...the large air hose from the air box to the turbo is subjected to a lot of heat (no heat shield on my car) and oil/gases sucked in through from the case. Over time, the rubber turns into goo and will actually collapse when you accelerate, again, choking the engine. The hose is expensive. But it may be repairable. I spread high temp, black RTV silicone on the outside and layered 4 to 5 pieces of aluminum foil over the effected area. This stiffened the hose AND acted as a heat shield.

    Good luck!
    Greg








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      motor won't run above 2000 rpm 900

      posted by  Felix_the_Cat on  Mon Oct 18 02:51 CST 2004
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      last visit: Wed Aug 13 14:16 CST 2014
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      wow, I can't believe that someone else had this problem, as it seemed almost unbelievable when it happened to me. I usually do all my mech work myself, but an imminent trip forced me to consign it over to my local (very trustworthy) wrench guy. I'm glad I did, because I never would have found the problem in a million years. In fact, when he called with a diagnosis I insisted that the he SHOW me the problem, 'cause I thought he was pulling my leg. There was so much goo in the intake from this foam that it actually glued my turbo in place and prevented it from turning at all, which provided the same symptoms ie 1700 rpm max, and absolutely NO power whatsoever. It took the poor guy six hours to clean it all out, but the thing ran like a champ when he was done, and not a single new part.








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    motor won't run above 2000 rpm 900

    posted by  porkface on  Fri Oct 15 15:27 CST 2004
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    last visit: Fri Oct 24 09:12 CST 2014
    [RELATED]

    check ALL the hoses between the turbo and the intake. any leaks or balooning will keep the boost from reaching the motor. the amm is another possibilty, given it runs better unplugged. btw, when it's unplugged, it cannot keep the fuel matched with the rise in air flow under acceleration, no way to talk to the ecm. good luck, chuck.








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    motor won't run above 2000 rpm 900

    posted by  spook on  Fri Oct 15 14:34 CST 2004
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    last visit: Fri Oct 24 08:06 CST 2014
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    Dear calvic,

    Good p.m. and hope you're well. What codes does the OBD (On-Board Diagnostics) show? The code reader ports are near the strut towers (not sure which side on a turbo, likely the driver's side, though). I'd be surprised if there aren't any codes. See the FAQs (under FEATURES, above) for how to access the codes.

    You might be able to re-set the Engine Control Computer. To do this, turn the ignition completely off. Then, remove the negative battery cable clamp from the battery terminal and put it in a plastic bag. Wait 15 minutes. Then, re-connect the negative battery cable clamp to the battery terminal.

    If there are no codes, and the ECU re-set doesn't help, I'm stumped, for the moment.

    Yours faithfully,

    spook







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