95 Sunfire Jerking/Bucking

[DesperateMom]

In the middle of Feb., the oil pump on my daughter's 1995 Sunfire Convertible (130,000 miles) went out. Two mechanics agreed that a new engine was required, and we had one put in, along with a new clutch pack ($3,650, plus $950 for a rental car, and $300 for taxis/shuttle).

After 600 miles, daughter took it in for the warranty-required oil change, etc., and Pontiac dealership noticed that it was unable to get any computer diagnostics--the message was "computer not connecting to (or communicating with) scanner," or something like that. They said they had no idea what the problem was, that it would take an unknown number of days to diagnose and repair. Since she wasn't having trouble with it, she decided not to pursue it at that time.

After 2,000 more miles, the car started to jerk violently in all gears. She took it to PepBoys, who first thought it was (1) ???, but jerking persisted; (2) the flywheel (it hadn't been turned when the clutch pack was replaced, and was badly pitted) - PB had it professionally done, but jerking persisted; (3) the O2 sensor (which appeared to be new to PB, altho not a normal part of the engine replacement effort, and was putting out readings in the thousands) - PB replaced the sensor and the readings became normal, but jerking persisted, and (4) the computer ($1,300 total to PepBoys, plus $350 for a rental car).

After replacing the computer, it still wouldn't connect to the scanner, but the car reputedly "drove like a dream." PepBoys test drove it three times, for 20 - 25 minutes each, and no jerking. (In the test drives following the ???, flywheel, and O2 sensor, they said 10 - 15 minutes into the drive, when it got "warmed up," it started jerking/bucking in all gears. Daughter and mechanic both described the jerking as feeling like when you're first learning to drive a stick shift.)

Three hours after daughter picked it up, and 30 - 35 minutes after starting to drive it, daughter had it on the highway, shifted the manual transmission into 5th gear, and it started the violent jerking/bucking again. IT IS **CURRENTLY** NOT JERKING IN ANY GEAR OTHER THAN 5TH.

Other than thinking there might be "a short," which they indicate could take days to locate, PB is out of ideas.

Daughter thinks it's the clutch because, when the clutch went out on a Mazda she had previously, it acted like this--first problematic only in 5th, then in 5th and 4th, etc. She recalls that she didn't have clutch problems before the new engine/clutch pack--we just replaced the clutch pack because it was convenient to do while the engine was being replaced--and recognizes that two mechanics have now worked on the clutch - when the new engine was put in a month and a half ago, and when PepBoys worked on the flywheel.

Daughter's boyfriend thinks its the transmission, but I ran that by PepBoys early on and they dismissed it, as did the two local mechanics we've been discussing the problem with, primarily because its a manual transmission.

Daughter is attending college over 1,000 miles away, and parents have now invested $6,250 in this (old) car in the past six weeks, and simply don't have the money to buy a replacement car, or continue to pay for repairs. OUT OF IDEAS AND $$$ - DIAGNOSTIC HELP/IDEAS/ADVICE NEEDED DESPERATELY!!