My car did the exact same thing, It would jump all over the place, from10mph to 120 to 60, then 0, sometimes it wouldn't work at all for a long time, I changed the VSS and it fixed the problem, Look on your tranny just behind your starter, there should be a 2/3wire plug back there that hooks onto a sensor that has 1-2 10mm bolts holding it down, some of the sensors come aparts in 2 peices( bottom peice is the mech part. top peice is the elec part) You can pick one up for about $40 on Ebay, my car is a 99 SI and I am using a sensor for a 94 accord. Im like 80% sure that your car has a VSS, look and see, look it up on ebay, search for VSS with your car modle. good luck..