I just had the same issue. I thought it could've been a number of things, but I decided to start with the ECT sensor. That was the problem. After changing that, the temperature gauge rose to the regular half mark, but it still takes five minutes to rise. I paid 27.00 for the ECT at the dealer.

I think there's a do-it-yourself guide to changing the ECT in the search somewhere. Check it out.

Some tips- most people seem to say that the clamp around the ECT is a pain to pull out, but using the hook part of a wire hanger I was able to just slip it out, no problems. Also, watch out for the breather hose!!! It seems to be commonly brittle and it costs 100 to replace. The previous own of my car broke the breather hose and put it back together with electrical tape... that sucked for me when I discovered it.

 

Thats great news that worked it for and i hope i get the same results. I went to autozone today to pick up the cts and it was the wrong sucking one. So im guessing i will be going to the dealer tomorrow and picking up the sensor. Autozone lists the completly wrong sensor for the car.

 

I finally got theright cts and it fixed the problem. I love my a4!!!