My B5 idle kinda rough, but everything seems to be okay except for the engine temperature.
If the car is idling the temperature gauage will be in the middle. In city driving it will be just before the middle on the cold side. However when I take the car on the highway it is also showing cold! Even if the the car is idling and the temperature is perfect, it only takes about 5 mins on the highway for the gauge to drop all the way to Cold.................any ideas?

 

Likely a thermostat problem.

 

Yep, I agree. Your thermostat is stuck open. That's why you get a bit of engine heat in the city but when you get on the highway, it cools right down. It should be a relatively inexpensive fix.

 

inexpensive if you do it yourself. V6 or 1.8L ? easiest/only way to do it is pop off the front bumper ,pull off a/c cooler and pull off the rad support/ radiator then 2 pieces of plastic. From here its behind the timing belt on the front of the motor on the V6. Pull the housing without getting rad fluid on your timing belt and you should be able to pull the belt aside enough to get it out.

 

I have the same problem, I just haven't gotten it looked at yet!