It's worst in 1st and 2nd, noticeable in 3rd, and barely noticeable in 4th, 5th, and 6th.

I run the gear up to 3k RPM, let off the gas abruptly - It feels like 3 little bumps while the car jerks/bucks forward and back and then runs smooth.
When I press the gas again there's a couple small bumps and then runs smooth again.

I've replaced the OEM lower motor mount, OEM upper stabilizer mount, and upgraded the OEM upper engine mount to a TSW urethane mount but the problem is still there.

It is the worst in bumper to bumper traffic. People must think I'm a newb at driving manual based on how much my car jumps around. Running 2nd up over 3K RPM and then having to let off the gas is the worst.

What could the cause be?

At 95k miles, I know my control arm bushings need to be replaced. My clutch makes a groan every few weeks on the coldest dampest SoCal mornings. Could either of these be the issue?

 

I have similar symptoms to what you have. I replace my control arm bushings over the summer, yours definitely need replacing and could fix some of the issue. I also have a poly a insert for the lower motor mount and still have a lot of drive train play. It could also be coming from a bad dual mass flywheel which is where I think the play I have now is. When I pulled the clutch over the summer I noted about 3 degrees of play, I would wager it has gotten worse.

 

I have a similar problem. I have a 1999 Oldsmobile Alero, and everytime I get the car to 20mph to 50mph and let off the gas the rpms on the car jump between 1k and 3k and continues to do it until I come to a complete stop. The car also accelerates on its own and sticks at around 25mph to 30mph sometimes. I have replaced my idle sensor, and have also replaced my throttle control sensor and cleaned my throttle body out. I don't know what else to do or what might be causing this problem. Can anybody please help me?

 

Read up on the "Yo-Yo" effect if you have not already, it has to do with the bypass valve. I have an 04 JCW and was having bucking issues when letting off throttle in 2nd and 3rd. the Detroit tuned BPV fixed it.

 

+1

Kevin