I started noticing some problems with one of my cars (1991 RS with a 700-R4), so here is a detailed description, maybe some of you guys could help me diagnose the problem.

So a few weeks back my tach started making very “frantic” movements. When idling or driving in any gear the needle would loosely bounce around the actual RPM. The very first time I noticed this I thought it must be the sending unit or something because despite what the tack was reading the RPMs of the motor were calm and constant. However shortly after I noticed this problem a second problem arose and I became confused. The car would shift fine through the first 3 gears but often times it would shudder into over drive. It was like the power was cutting in and out. Sometimes it would take several seconds for things to smooth out.

My initial and unfortunate thought was that the transmission was slipping, however because of the problem with that tach and because transmissions work sucks I would like to think it could be something else.

Any thoughts? Is there any particular way I can drive the car, say up a steep grade or accelerate hard that will help diagnose the problem? I would really appreciate any insight into this problem. Thank you in advance for any help.

Sounds like it might be the Lock-up Converter, but not sure.....Good Luck, Tom

I have about the same problem, but it's been doing it for almost 2 years. My guesses for mine is VSS, my speedo doesn't work, overdrive switch in the transmission, loose wires, or the torque convertor. Maybe you have one of those not acting right.