ok, there may be a couple different possibilites for this to happen. its starting to look like a transmission glitch. let me start out by saying whats goin on with my car right now. there is a problem with the cat. converter. its probly a bit clogged(stuff is loose inside, im 90% sure of that now). My car had a slight "fluctuation", which i thought was misfiring/fouled plugs. i changed the plugs/wires. at the same time, i put on a FWI and 3.5 pulley(with one heatrange colder plugs). then my cat started rattling/engine running a bit rough. and now, ive been noticing that the car is still "fluctuating". actually, its turning into a "jerking", almost like i was tapping my gaspedal foot. it ONLY happens when the engine is under a load, like in top gear in just above 1,000 rpm to just under 2,000 rpm, especially uphill. if i "get on it" some, even a little bit, its fine. could it be my somewhat clogged exaust? or is my transmission having shifting problems? fyi: i will be fixing my exaust problem this week hopefully.

I would bet on the cat. I had a 1990 supercoupe that was doing the same thing as you're describing. I took it to the ford stealership and they said it was the head gaskets. I took the car to a mom and pop exhaust place and had it fixed for $300 ish instead of $1400 and not fixing the right thing. -Ron

i may have found the problem. i checked my transmission fluid today. it was halfway down on the dipstick. my original trans pan gasket was tore up some, so i used the cork one that came with my filter kit when i changed the fluid last time. that was about 30k miles ago. so its been slowly leaking i guess. i was already planning on changing the filter/fluid again, but i just ordered a felpro "hard" gasket(30 bucks ) and put some of the dexron 6 i just got in. it seems to have helped alot. i can tell i still need to fix my exaust and change the fluid in the pan, though.

well, i changed my tranny fluid. I used almost 8 qts to fill it back up, so a good portion of the fluid got changed. i notice a difference in shifting, its much smoother now. it had some sludge on the pan/filter, though. i cleaned that off. the "jerking" thing is still happening(it only happened once, though). it still seems to be lagging some(because of the exhaust im guessing)still. i'll hopefully have somebody install my replacement cat/downpipe this week to see if thats it.

well, i just got a nail in my rear tire. i guess im not fixing the exaust yet, gotta buy tires....

alright, i gotta resurrect this thread. after changing the tranny fluid, putting on a highflow cat and downpipe, my car still does this jerking chit. it may be something with my transmission, like the torque converter or the line pressure solenoid(as someone at stlclubgp suggested). it just started throwing a ses code, P0420. the printout from auto zone said that cylinder bank #1 o2 sensor is reading insufficient catalyst or "dirty air" and that two causes could be a misfire or vacuum leak. im changing my plugs(again) right now, ill see if that fixes the problem. the plugs ive pulled off sofar look to have "normal" color. also, i dont know if its related, but as i was reaching back to change the back plugs, i noticed liquid on top of the LIM, underneath the supercharger snout. its pooling towards the back, though. i think its coolant by the look/smell of it. anybody have any ideas on what else could cause that code if changing the plugs doesnt help(which i fear will not)?

ok, i took it for a test drive after changing the plugs. i was all exited because thought that fixed the problem. i drove it under conditions that would have made it jerk before(uphill, in top gear at lower speeds) and it didnt, at first. on the way back to here, it started doing it again. it seems milder, but it still does it. should i clear the code and see if it comes back?

With the discovery of the coolant, it is quite possible that you have a LIM gasket failure. That could very well cause the problems that you are experiencing.