my temperature gauge only moves when im driving and then i turn the car off and then back on. i dont no whats wrong i brought it to my mechanic and he told me the car was fine. i have 98 a4 2.8

 

Most likely the coolant temp sensor has failed (it's common on these cars). It's a $25 part and isn't hard to change. Check www.audidiy.com or www.audiworld.com (in the Tech area) for DIY procedures on how to change it. There are three types, identified by color (black, blue, and green). The black sensor is the oldest, and was replaced by the blue one. The green is the newest type. I have a blue one in my 99, and you probably do too. Call www.ecstuning.com and give them your VIN number and they can order the right one for your car.

 

Your Temperature gauge is working as intended. If you would like to throw a bunch of money at it just to find out nothing changes is up to you.

Good Luck...