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Engine Rpm's Varying wildly above 40 MPH without acceleration 850 1994

posted by  Matt P on  Wed Aug 20 14:57 CST 2003
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I have a 94 850 Turbo with 117K miles. I was driving about 55 miles per hour, I let go of the accleration, and just let it move at the same speed. The RPMs went down to 1500, and then quickly back to 2000, and then back down to 1500 again - in the process speed dropped. When I accelerated back to 55 the acceleration was not smooth and constant.

Normally without acceleration the RPM would stay at 2000 at 55 MPH, and remain there with at a constant speed.

The other day, when I was driving at 40 miles per hour, the rpm swung wildly from 1500 to 2500, and then to 2000. I was feeling my car lurching - slower, faster, slower. The car couldn't decide what gear to stay in.

Any ideas what could be causing this? The strange thing is that there are no lights that came on at all. I assume that means that there are no codes stored to explain what is going on.








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    Engine Rpm's Varying wildly above 40 MPH without acceleration 850 1994

    posted by  CmdrPrang on  Tue Aug 26 09:36 CST 2003
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    this happened to me too recently. i was on the highway, blazing along, let the foot off the gas to maintain speed, observed huge fluctuations in rpm.

    in my case, the rpms flying up were due to the transmission downshifting into an inappropriately low gear. the downshift was caused by the engine stalling, fooling the computer into going back into lower gears. the stalling was accompanied by very rough idling. the solution to my problem was fuel system treatment and cleaning the gunk out of the throttle body. no more stalling, no more shifting problems.

    best regards,







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    Engine Rpm's Varying wildly above 40 MPH without acceleration 850 1994

    posted by  brickbat on  Wed Aug 20 16:59 CST 2003
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    Has a similar sympton with my '96 turbo. Fixed two things and its cleared up: first was a really gunked up idle air control valve - was able to clean this up with throttle body cleaner. Other thing was a leaking canister purge valve - had to buy a new replacement for that. The bad purge valve was causing other symptoms, such as stalling while idling.






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