Power loss and white smoke

[George Fairbanks]

Hey guys,

I'm hoping that one of you can help me diagnose a problem I'm having. 
I've got a trustworthy local mechanic but he's not a 200 expert, nor 
even an Audi specialist.

A bit of history -- probably three years ago I started the car on a cool 
morning and, for the first time, it put out a puff of smoke out the 
back.  Since then the car has had a stinky exhaust when first started 
after sitting but it passes emissions just fine when warmed up.  My 
mechanic guessed that some oil was making its way past the turbo and 
being burned off when first started.  The car hasn't been using a 
noticeable amount of oil.  I've been getting an indicated 1.7 bar of 
boost for a few years now instead of 1.8, but haven't been bothered 
enough to look into fixing that.

Some of you might know this car as it's Greg Amy's old car.  It's been 
running without incident for the past five years here in Pittsburgh 
while I'm working on my phd.  It's got 193k miles on it now and I 
believe Greg's had the chip in there since about 100k miles.

This past weekend I was accelerating hard (honestly, I don't do this 
often as I'm stuck in Pittsburgh, the city of potholes and I have 
cracked one rim here already) and heard a funny noise coincident with a 
dip in power.  The noise was sort of like a "grunk".  When I restarted 
the car about an hour later (I did let the car cool down before parking) 
the car put out enough whitish smoke to really scare me.

When the smoke went away after a couple seconds, however, the car ran 
fine for the rest of the day and for the return leg of my road trip (240 
miles).  Gas mileage on the trip was normal too, 27 mpg on the highway.

I have heard this grunk noise a couple times before but had chalked it 
up to mid-grade gas when the chip requires high octane, but was only 
half convinced it was premature detonation.  Now I really don't think 
that's it.

Any ideas on what the problem could be?

Thanks in advance,

-George