Bucking at low speed

Discussion in 'General Motoring' started by rslakey, Nov 29, 2003.

  1. rslakey

    rslakey Guest

    Hi. I have a 1992 SL2 Saturn. It has 107,000 miles on it. For the
    last 20,000 miles or so, it has bucked on acceleration, particularly
    when warmed up. (It bucks when cold, but only mildly, and because the
    idle is up higher, the bucking is masked.) At highway speed I can
    sense a miss, but the speed of the vehicle smooths out the bucking,
    and it is hardly noticeable - but it is there.
    I have replaced the plugs, used several bottles of injector cleaner,
    replaced the in-line fuel filter, resistance-checked the spark plug
    secondary circuit, verified that the fuel pump is within tolerances
    published in Haynes, and verified the proper operation of the EGR
    valve and fuel manifold pressure relief valve. I have also replaced
    the accelerator cable.
    The "Service Engine Soon" light is not on. There is nothing logged on
    the car diagnostics computer that I can find.
    The car may be getting about 2 miles per gallon less than it did
    20,000 miles ago, but I can't be sure - it gets about 28 mpg today,
    combined driving. I don't know if this is related, but when I engage
    the cruise control, there is a temporary increase in engine speed and
    road speed (to the tune of about 4 mph), before it settles down to the
    selected speed. (Settles down in about ten seconds.) Cruise works
    perfectly after that.
    I am lost for ideas. Anyone got any ideas?
    rslakey, Nov 29, 2003
  2. did you replace the air filter? maybe that's clogged, or your throttle body
    is fouled or something like that - I would try removing the airbox, cleaning
    the throttle body (make sure the plate is clean on both sides, and operates
    smoothly - carb cleaner works well for that), then reinstall the airbox with
    a new air filter. Also, if there is some sort of aux. air valve/idle air
    valve/etc. make sure it is functioning properly and not fouled (also make
    sure the intake leading to the air filter isn't plugged with leaves or
    something like that). Another thing to check would be electrical
    connections - I would de-mate, clean, and re-mate all of the connectors you
    can find, then disconnect, clean, and re-connect all of the ground
    connections (not uncommon for oxide buildup or other crud to increase
    resistance and mess up electrical performance in a car - esp. after 11
    years!). Could also be a bad injector... Another potential issue - if the
    car uses a MAF sensor, it could be fouled and need to be cleaned (clean the
    wire very, very carefully).
    David & Caroline, Nov 29, 2003

  3. You too? My '93 SC2 is doing it too. I've yet to try plug wires, it
    seems ignition related. I'm wondering if it's the MAP sensor - my
    harley did this when I once unplugged and didn't replug the sensor, but
    on the saturn, I don't know if MAP affects the ignition...
    Philip Nasadowski, Nov 29, 2003
  4. rslakey

    BANDIT2941 Guest

    Hi. I have a 1992 SL2 Saturn. It has 107,000 miles on it. For the
    How old are your plug wires? That'd be next on my list.
    BANDIT2941, Nov 29, 2003
  5. This is likely an ignition problem, such as voltage leakage from the plug
    wires, or carbon tracking of the ignition coil(s)..
    Robert Hancock, Nov 30, 2003
  6. rslakey

    BANDIT2941 Guest

    That reminds me. I had a coil go once, actually it might have been the module,
    I'm not sure(I replaced both coils and module with a unit from salvage yard).
    The car bucked like crazy. Like I said before, try spark plug wires first. They
    aren't that much $ and by the sounds of things you might be overdo for a change
    anyway(ie, if they don't fix the problem, you didn't waste your money). If I
    may suggest, get a set of Accel wires from NOPI online. I think they were
    either $26 or $29. All the plug wires I bought from stores like NAPA and
    Autozone(and I tried like 4 or 5 diff sets) leaked voltage after a month or so.
    The Accel's are cheap and so far are holding up good.
    BANDIT2941, Nov 30, 2003
  7. rslakey

    Dan Hicks Guest

    This is where taking the car to a shop with an ignition analyzer may
    pay off. They can detect a number of problems with ignition and
    fuel that won't set (useful) codes.
    Dan Hicks, Nov 30, 2003
  8. rslakey

    rslakey Guest

    Hello to all those who had ideas. I have replaced the wire set - no
    help. I also forgot to mention that I had replaced the EGR solenoid
    for something else - a code 26 at speed. Anyway, I also verified the
    operation of the injectors - all are clicking, and not missing a beat.
    I decided to go for broke - a replacement of the oxygen sensor.
    That fixed it. Smoothed right out, and power is back.
    Thanks to all who provided insight!!
    rslakey, Nov 30, 2003
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