Smells problem
1993 Toyota Previa Two Wheel Drive Automatic 136660 miles

Speedomoter showed 70, radar-gun said 87. Had sensor replaced. A few days later the Speedometer is still not accurate. Shows 0 mph, or sticks on 10, 15, 25 mph, when I'm actually going faster. It's scary because I don't know how fast really going; and I don't want to get another ticket! HELP! Mechanic said connecting wire was loose, and he fixed it. A week later the same problem comes back. Now the mechanic says the head is probably what's wrong, but I don't trust him anymore for various other reasons. What could be the real problem? Thanks!