Some times my temp reading in my 98 A4 1.8T QM starts to go down to like negative 50 when its +65 outside.. anyone had a similiar problem or know what might be going on?

 

check the ambient air temp sensor, behind the front bumper. unplug it and check your reading, then jump the terminals with a test lead or a paperclip and check the reading again. one should be a really low number and one should be really high, cant remember which is which, sorry. if so then the circuit is ok; replace the sensor. if not, there is another problem.