The speedo in my '04 Z is peged out and does not work. It started by getting stuck in no certain place then it would start reading from where it was stuck or it might not work at all. If I put it and gear and hit the starter if will jump back 5 mph at a time till I get it to zero, it might work for 1 min. or 1 day. If it is working it is still accurate no matter what position it is in. Does anyone know where to start troubleshooting?