My ambient temp starts off with a reading 10 degrees too high, and takes a few minutes to correct itself after starting. It makes no difference if the car is parked in the garage or not.
Why is this so?

 

Hmm, I'm not sure why this is. The ambient temp on my car seems to read just fine. My guess would be that there is a faulty sensor, or something or other, but I'm not too sure. Have you taken it to the dealer?