speedometer jumping?

i have a 2001 explorer sport trac and when your sitting still and the truck is running the speedometer bounces between 0-20. Does anybody know anything?

I know quite a few things, if I do say so myself....

Oh, I suppose you mean with regards to the jumping speedometer in your truck. Sounds like you either have a bad connection in your instrument cluster, a problem with the wiring for your vehicle speed sensor, or a bad diode (or more) in your alternator. Are you experiencing any other issues such as an ABS light that comes on randomly or stays on? Does your cruise control work?

-Rod

Yes the cruise works. The abs light comes on randomly. The O/D light comes on and flashs sometimes.

The vehicle speed appears to be sourced from the ABS system on your Sport Trac. The ABS provides wheel speed to the PCM, and the PCM feeds the speedometer and cruise. If your cruise works reliably, even when the speedometer does not, I'd suspect the issue is either a worn speedometer head itself or a connection issue to or within the instrument cluster.

-Rod