Dynetik

Whats going on Toronto Integra's I have a 91 integra with a B16A (1st Gen) swapped motor, when I first got the car the idle speed would always be around 1800rpm then drop to 800rpm (nothing was wrong atm)... Now my car recently started overheating so I changed the thermostat + had to re-wire my temp gauge (it didn't work at one point)... and after changing it the initial warm up was the same as before. 2 days ago the idle jumped to 2300 or so rpm's and when the car was warm, when driving for half an hour or so the temp gauge would go alll the way up to HOT then descend to less than half... !!! My 2 questions are: Is it "normal" for the engine to idle that high after seeing it idol below 2K before & why was my temp gauge acting all possessed ??

Any ideas, suggestions would be greatly appreciated !!!