rough running

[retired mechanic74]

....Has anyone experienced a 1989 Reatta when after closed loop shifts into 4th gear and the toque converter engages the car responds like if it were a manual shift and your going to slow in 3rd gear and the engine bucks and jerks but when you press down on the gas pedal the car downshifts into 3rd and runs great. The car is fully tuned with all new parts and one injector replaced.  The car runs great as long as it doesn't drop into the converter clutch. If I disconnect the wire for the clutch at the transmission I have no problem.

[Ronnie]

My neighbors car, a '90 model Olds 98 with the 3800 engine, would do the same thing. When we took it for a test drive it would do it every time on the same long, gradual hill if you tried to accelerate up the hill. When the torque converter unlocked or the transmission downshifted it would stop. We replaced the Ignition Control Module (complete with coils) and if fixed the problem. If you haven't changed them already it could also be the spark plugs or spark plug wires.

 

When the engine is under load at low RPM is when the most stress is on the ignition system. When the torque converter or transmission downshifts it reduces the load on the ignition system. That is why the bucking, (caused by a miss) stops.

 

You might be able to reproduce the miss in the driveway by holding the brake TIGHTLY with the transmission in gear and applying a lot of throttle.

 

Hope this past experience of mine will help.

[2seater]

I think Ronnie has it right on the head. Classic symptoms of ignition breakdown. If the plugs are gapped at .060", you could try closing them up to around .045" to confirm.

[DAVES89]

I agree as well, however some consideration should be given to the Mass Air Flow Sensor. I had a bucking situation swapped it out and problem corrected itself.

[RedRacer]

I am very thankful for this post- my car has started doing the same thing - now I have some ideas what to check!  Thanks.