My speedometer in my 90 Deville has been acting up for over a year now, getting worse (standard speedo, not digital). While driving and after the car has warmed up, my speedometer needle starts swinging madly back and forth. It will sometimes stop on zero for a few seconds, then pop back up to current speed (and it usually only happens on the freeway during steady, high speed - usually, not always), back to zero, back to current - sometimes not stopping at all, just swinging back and forth. When it very first started it was always in the hot afternoon during summer. Now it's doing it when colder out and more frequently. It doesn't ALWAYS happen, it's very random. I understand these are quartz speedometers controlled by electrical pulses from the VSS. Is this fixable or yet again, another replacement? I've not been able to tell if the odometer stops rolling while this happens, I can't take my eyes off the freeway at 80mph that long!