Get you battery checked first. I have had a few cars that had the battery going, but not bad yet, and the symptom was the gauges fluctuating just like yours. If you have the original battery it is likely time to replace it. I just put a new Interstate in my Aero. The cars now a days are VERY picky about the voltage and current they get and if it isnt up to par they start doing odd things. Good luck.

MikeR