On my 91 RS the speedo will sometimes just stay at 0, other times it's right, and other times pegs and stays while driving. In any case the cruise works fine. Are there separate speed sensors for cruise and speedo? Where's the one for the speedo. Probably a loose/intermittent wire that I need to check. Thanks!

 

No, there is only one speed sensor. The vehicle speed sensor (VSS) is located on the tailshaft (on the back) of the transmission on the driver's side.

It does sound more like a wiring problem. Most of the time a failing VSS or buffer causes the speedo to just quit working altogether. But, first, have you checked codes yet, mainly for a code 24? You can learn how to check the codes in the FAQ on the main page (if you don't already know how to). Also, something else that may help, if you have a friend or know someone with a scan tool or a laptop with WinALDL, and see if the computer is seeing the same MPH that the speedo is reading. Just because if it's just the speedo that's off, than you can seriously narrow down the possible problems.