so my friend has a 1991 acura legend his wife wants him to get rid of. it's an automatic, decent body, but just needs it off the road. not sure on miles, we didn't discuss it much. It has a dead battery (not a problem) but there is one problem. The speedometer spins randomly. it doesn't match the vehicle speed. I guess it just jumps erratically. what would cause something like this and is it an expensive fix?