Had just installed the GT3 front bumper and noticed there are some great vartiations on the outside tempterature. Last night temp was around 88 here and the reading showed 97 when I started the car. After driving a few minutes temp adjusted to normal but would swing +/- 2 degrees every few inutes. Just a crazy glitch or something I need to look for? Thanks.

 

My Carrera has a highly irregular temp readings as well. I love getting into the car and the temp says 107 in the summer when it's 92 outside (probably from the excessive summer heat in FL cooking the bumper) but "settles" out after driving around. It tends to be more accurate in the wintertime and on cloudy, rainy days here in S FL. Not as accurate as my Lexus which is usually spot on. It's similar to my oil pressure (idiot) gauge which always rides at 4-5 except at idle.

 

I don't know where the outside air temperature sensor is on a GT3 bumper but on a OEM 997 bumper it's located in the passenger side duct. I suspect it somewhere close since the cable restricts where it can be located.

It's a flexible rubber sensor that pokes through a hole. I'd check that it's properly attached before I do anything else.

 

I assume its similar to a 996, mine was acting really funny (gt2 front bumper) and it was because the sensor up front was stuffed behind part of the bumper (its just a little rubber cone looking piece, I simply pushed it to the side where it can get some airflow). The sensor needs to have air flow across it to work properly, I would check to make sure its not blocked since you changed your bumper.