I remember from when I had my 2001 A6 2.5 Tdi that the MAF's on these engines are problematic. Albeit, that engine was the 155bhp fwd model.
The MAF on my A4 2.5Q is faulty. It is currently a Hitachi brand. I've seen that there is also Bosch and Pierburg brands available. The bosch unit was on my 2001 A6, changed twice in 18months!! Luckily the second time it was replaced under warranty by Audi as the new failed 6months into use!!
What is the preferred choice for the 180bhp lumps?
Can you just buy the actual sensor to fit into the metal body like you can for the plastic bodied mafs?