I have a 2002 Honda Civic EX. My problem is that the temperature gauge goes up and down without any reason. The car does not overheat. The A/C and heater work fine. The gauge just up and comes down almost as fast as it goes up. Help

 

That's sorta normal with any engine. I hang mostly over at the VW TDI forum and they all complain because the temperature gauge has like a 20˚+/- buffer built in.
Just do a general evaluation of the whole coolant system, old coolant, partially clogged radiators, sticky thermostats and especially small leaks will cause fluctuations in temperatures.
Does it go out of range hot or cold?