alright I searched and found nothing specific to my problem so here it goes

I am driving down the road at about 3k rpm's....and all of a sudden my speedometer moves up and down then completely stops and the car starts sputtering....I let off the gas...and its alright for a few seconds then goes right back to sputtering again.......let the car sit...the next day it will drive fine...it just comes out of the blue sometimes.....what in the world could be the problem?.......what gets me is the speedometer/sputtering combo...wtf?

thanks