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    Hesitation/stumbling in mid range

    So my mechanic is working on a 90 325i, and it has a wierd hesitation between ~2800-4000. It is most noticable under more load (3rd, 4th, 5th) but that could just be because it shoots through the low rpm too quickly in low gears.
    I tried WOT, 3/4, 1/2, 1/4 throttle, it is there no matter what throttle position. It is not a serious miss, it is not bucking (hard at least), it just surges a little while climbing through the rpm.
    It idles fine, has loads of power, and is fine at anything about 4k rpm. But the owner is an old lady who never floors it, so she's constantly sitting in the zone where it just hesitates and the car just surges while holding constant rpm.

    We've changed the in tank pump, fuel filter, wires, plugs, cap, rotor, o2 sensor. Tried a different AFM, tried different ECU's (153,173,380). Cleaned crank sensor and toothed wheel.

    Any ideas?

    #2
    maybe coolant temp sensor? I would not think it is fuel related if it gets better after 4k rpm. Doesn't sound ignition related if it has a good stable idle. I would think it is sensor related. Maybe get it on an engine scope. Have you adjusted the valves? A long shot but may be worth looking into.
    sigpic
    1991 325iC w/ 75k Original Miles, Brillantrot, 5-speed, 16" BBS RX's, Black Leather Sport Heated Seats, LSD, and Diving Boards for life!!!:D

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      #3
      Fresh valve adjustment + valve cover gasket

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