Bouncy speedometer

[tseak]

So this morning as I pulled out into the streets, I stopped at a red light and my speedo was bouncing erratically, and came to a stop at ~82mph, while I was at a complete stop. Then as I drive off, it bounces erratically again, comes down to 0 and then resumed normal function. This happened at every stop. So I pulled over and restarted the car and everything was back to normal. Anyone have any idea what might have caused this?

[liigod]

Mine has done the same thing 3 for 4 times over the last year or so. I have no idea what it is.