When you drive it it surges and the speedometer does not work?

This van sat for a year with a dead battery. I got it running and now when you drive it it surges and the speedometer does not work. What could be causing this. I am thinking maybe the speed sensor is not working and throwing the computer out of whack. I dont know where it is located. Or what else could be causing the problem?
please help!
thanks,
ryan