Edit:: 180 beat me to it, what he said :P

That is outside temp, the car needs to be moving for it to accurately report the temp, it should not be jumping all over the place though. Chances are it came loose. Check the lower grill on the drivers side, that is where it is connected. Should be mounted close to the middle if I am remembering correctly. Yours may be dangling back in there some place and not reading properly.