Speedometer Gone Wild!!!!

While driving my 1998 Jimmy today going about 75, the speedometer needle would bounce back to 50 then to 75, back to 40 then back to 75 & even to 0 and back. Occassionally the engine would slow down in response. This action was random and would stop for a time if I stopped, turned off the engine and then restarted the engine. In addition, the ABS light would also come on but not everytime this action started. I believe it may be a sensor problem but I am a RN and not a mechanic. Would like some ideas before I go have the car checked so I know how to evaluate the info I receive from the mechanics.

Thanks in advance.
LeeS

While driving my 1998 Jimmy today going about 75, the speedometer needle would bounce back to 50 then to 75, back to 40 then back to 75 & even to 0 and back. Occassionally the engine would slow down in response. This action was random and would stop for a time if I stopped, turned off the engine and then restarted the engine. In addition, the ABS light would also come on but not everytime this action started. I believe it may be a sensor problem but I am a RN and not a mechanic. Would like some ideas before I go have the car checked so I know how to evaluate the info I receive from the mechanics.

Thanks in advance.
LeeS

The only vehcile I have owned and experienced this problem on was my old motorcycle, and all I had to do there was replace the speed-o cable. The cable looked good, but even the smallest bind in it could screw it up. Now I am not sure how your 98 Jimmy is setup. But that would be my first guess.
Hopefully someone else will have more insight on it.

Anything from 89 up on our trucks are electronic... The speedo is controlled by the VSS via the DRAC module... So more than likely it's your VSS on your tranny (vss=vehicle speed sensor)..

I experienced something similar with my 96 Jimmy last year. I was pulling out of a parking lot and had my speedo go crazy. Turned out to be a dying alternator not giving the computer the right voltage. If your having a slow turnover when starting, or any other lec type problems, stop by Sears or the such and have them test the alternator.

I have a 98 that had the exact same problem. I took it to the dealer because it would keep disengaging the cruise.The dealer blamed my remote start alarm, but since I had an extended warranty they replaced the turn signal lever which includes the cruise control. The dealer also replaced the instrument cluster a total of 3 times. After each replacement it would work for a while. After that I asked what else could it be. They suggested the VSS, the speed sensor in the transmission. Since that was replaced over a year ago I haven't had the problem.

Save yourself some time and have the speed sensor replaced.