My speedometer went crazy!

[supercharged1.8]

I was driving home this morning from work and as I was pulling into home I looked at my speedometer and the needle was jumping around spastically. At points it would jump all the way up to 140 mph It only occured when I was doing under 20 mph. When I got going it stopped but came back when I started to slow down again. Everything else in the guage cluster works fine. It did rain quite a bit yesterday and I accidentally left the passenger door window down about 2 inches. The carpet, seat, etc. was pretty wet by the time that I remembered to get my dumb ass out there and close the window and put the car in the garage. What do you guys think?

[318ispower]

Mine does the same thing and I dont know whats the cause of it. It only happens periodically but I guess there is nothing wrong with it.

[supercharged1.8]

Yikes. Man I want the thing to work right. I wonder if I got something wet? Hmm. I just dont want it doing that stuff, you know? I pride myself on taking care of my car and having it look nice, and work correctly. I have a VW GTI 1990 (daily driver) and I give a crap less if that car does wierd stuff, but my bimmer needs to work right. Anyone else have any ideas? Thanks

[supercharged1.8]

Does anyone elso have any ideas about this? Please help

[bimmer95]

Probably it's the speed sensor that bolts in to the back of the diff.