I drove up north on Friday which is about 120 miles on the freeway. The car drove fine for the initial 90 miles, but the last 30 the car was surging while cruise was engaged. The speedo never moved from about 73, but I hooked my laptop up and my digital speedometer (reading from ECU) was going from 70-75 and back. Also, my estimated load value was changing as the speed did.

 

No CEL and no driveability issues, and it did the same thing on the way back; fine for most of the way, then surging and ECU speedo bouncing.

 

Is this related to the speed sensor at the transmission, or something else entirely?

Speed sensor on the trans just drives the speedometer in the cluster. There's a converter in the cluster that cuts the signal in half and then sends it to the ECU.

I would suspect that since you say the speedo needle never moves.

 

Just out of curiosity though, did you turn the cruise off and see if the reading still changes the same way?

Now that I think about it, there has been some "stepping" of the speedo needle under heavy acceleration, as well as some whining that I know is the speedo cable... Guess I need to get in there and check it out. Hopefully it's simple like lubing the cable.

On a 97? There's no cable. Legacy went digital in 95.