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car occassionally bucks pretty heavily

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    car occassionally bucks pretty heavily

    hey,

    i have a friends e30 with a few issues. i did a few things off the bat, there was a thumping noise from the rear. turned out to be a loose tire. :???: main relay was bad, you could tap on it and the car would turn off. i swapped over all the relays in that bank from my car. (main, fuel, and that other one. heh.) and the car drove a lot better. for instance, the car would turn itself off and then back on again while driving. main relay fixed a few issues related to all that.

    but it still bucked really badly. like when a beginner is starting to learn manual and they cant get the car started smoothly. but it will happen while driving along. if you let off the gas, it will stop bucking though. a different friend of mine (also has an e30) thinks it's the transmission. but it happens in every gear, so im prone to believe it's not. if it was 2nd and 3rd, which generally take a good amount of abuse, ok. but 4th? ehh.. ANOTHER friend (also has an e30, im surrounded) suggested it was the CPS. although it had already been tested by friend 2 and he said it was good. it probably ran ok, but while removing it the wire came off the sensor. so it was probably due for a replacement anyway. it still bucked too.

    so im at a loss. all the spark plugs have recently been replaced as well. and unfortunately its been sitting for a long long time. 6 months, with half a tank. which was filled to a full tank 3 months ago. ... so the gas is probably halfway bad. but i've never had a misfire that jerks the car that violently. i mean, it jerks the car so violently, that the abs light turns on? i did disconnect the abs relay under the dash to see if it made a difference, like perhaps the abs was randomly hitting the brakes to full lock. but it didnt. im at a loss.

    any help is appreciated.
    AWD > RWD

    #2
    Maybe a vacuum leak due to cracking hoses?
    1989 US E30 Cammed S52
    Under Construction: 1983 Euro E28 Cammed LQ9/LS3 Heads/Jakeb E28 LSx Kit

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      #3
      the car does have a vacuum leak. the throttle body to the intake manifold does not have a gasket. but that is a constant leak, and this is an intermittent problem. also, unplugging the afm does not fix the issue. but i will get a gasket in there, or at least rtv.. lol.

      i swapped my dme into the problem car, and the car ran fine for 5-7 minutes with no issue. i thought i had finally found the problem, but as i was about to pull back into the driveway it started bucking again...

      alternator, rotor, battery, replaced cps, and coil all tested ok.

      coolant temp sensors were out of spec. should have been 300-360 ohms warm. was 180-190. those will be replaced. could this be it?
      AWD > RWD

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        #4
        The ABS ligh coming on when the car is misbehaving sounds like a problem with the primary distribution.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

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          #5
          what do you by the primary distribution?

          spark plugs, wires, etc?
          AWD > RWD

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            #6
            (this is kershaw, on friends account.)

            Thanks, I replaced the distributor cap and rotor and the car runs perfectly. The rotor was so trashed the metal was worn past the plastic. The cap was equally bad.

            Jlevie, I swear you are an E30 god :)
            -David

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