GM / General Motors: bucking/misfiring/hesitation problem

howdy, group

i have an issue with my automobile. i purchased a 1992 buick lesabre v6 from
my brother's brother-in-law about three months ago for a steal. very nice
car and so far, it's done its job.

i recently had some tune-up work performed on it: new plugs, wires, and fuel
filter. i had some drivability issues (some misfiring and overall not
running as smooth as it should have been) so it was a good time anyway. the
car ran very smoothly. however, i have begun to notice something "annoying".

what seems to happen from time to time is a bucking/misfiring problem. the
car will be running well for a time, then suddenly it will start to "buck"
as though is fuel-starved or misfiring. at this point, firmly hitting the
gas brings it out of this state. it seems to happen erratically (sometimes
it doesn't do it at all, other times it does it more than others). i can
best describe it in detail like this:

i will be cruising along, at which point it will feel as though it is
kicking into high gear. at this point the car runs a bit rougher, and the
bucking begins. so, i drove the car in "regular" drive instead of overdrive
(in this car, overdrive should be the normal "setting") to see what would
happen. it seemed to run better, leading me to believe that the problem may
be with the overdrive. i did also observe that occasionally while driving up
a steep hill, the problem would occur.

it's hard to explain exactly when it occurs since it is sporadic. i dropped
some "heet" in the gas tank in case water was in the tank, and have tried
higher grade gas for the heck of it.

i also pulled the codes. the only one that came up was code 43: ESC
circuit; knock sensor signal. not a clue what that is =) could that be
causing the problems i have mentioned?

as a side note, is it safe to drive the car in "regular" drive as
opposed to overdrive both on side streets and the freeway? just curious as i
have a fairly long trip coming up very soon

i have no other noticeable problems.

any help would be greatly appreciated.

thank you in advance!
scott

Same problem on a 91 lumina with the v6 turned out to be a bad vacuum
line. After it was repaired it ran fine in overdrive. It took a
while to convince my dad, even after he had it tuned up thinking it
was the engine stalling.

Pittd