Got the new battery in today, car started right up. when i turn the car on (cold start) the tach will start out at about 7-800rpms just idling, then jump up as it is running (before it gets warm). goes from about 7-800 and spikes up to about 1300rpms (fluctuating from 800rpms to 1300, back down, then back up), just the tach, not the motor. The volts on the gauge cluster also goes from around 13.8 and spikes to 14volts. any ideas at what is causing this?