Go on have a guess before the garage do...

[avspider]

I have a 96 A4 avant tdi (afn). Recently the mpg has been down, I have noticed when it's cold there is a slight blow from the exhaust, its not something i can do at home, so it's going into the garage next week... any idea's prior to it going in as to the problem?

Also the temp gauge seems to fluctuate a bit recently, it used to sit at 90 or a fraction under no matter what. Now it seems to fluctuate, it max's at 90, sometimes only sitting at 70.

Cold starting... when it's really cold, it's turn over a few times before it starts (the colder it is the worse it is), then there is a puff of white smoke out the exhaust.

[Padwick]

There's a cold start valve built into the fuel pump which I've seen failed on these engines before. It had actually failed before the car was purchased but the problem was hidden by advancing the pump timing, which created it's own set of problems.

Also, on most Audi's of the era, the coolant temp sender has failed and needed replaced.