Both the speedometer and odometer quit working. When started the speedometer automatically jumps to 20mph and stays there most of the time. Every once in a while it will kick back on and works fine, reads accurately, but never for more than a few minutes, and when it does the odometer works again as well. No idea what to do

. Check all under dash fuses with a test light or multimeter.

. Replace the Vehicle Speed Sensor (VSS). This is the most likely cause of your problem. Remove VSS connector, which is located on the transmission close to the firewall; remove both mounting bolts; and gently remove and replace the VSS. Replace VSS connector and the speedometer and odometer should work.