When starting after being parked for several hours, my '97 A4 1.8 emits a huge cloud of dense white exhaust smoke. It's definitiely oil smoke. It stops smoking after running a minute and doesn't smoke while driving. My theory is a leaking valve stem seal, which allows some oil leakage down into a cylinder. After the leaked oil burns, it won't smoke until the next time it sits for awhile and more oil drips down into the cylinder. The dealer doesn't agree with this theory, and has replaced a control unit, which didn't fix the problem. I'm getting ready to bring it back in.
Has anyone else had this symptom? Any ideas?

Are you sure it is oil? Does it smell like oil? White is typically coolant.

Try taking off the hose to the bottom of the intercooler (from the turbo), wipe a white paper towel. What do you find there?

It could be the stem seal, or the turbo, or something else. It might just be too warm to see the smoke once the car is running (gunk vaporises).

I fried two turbos in my '89 Dodge Colt Turbo, and the first indication was clouds of thick, white smoke.

Hopefully, for your sake, that's not it, but I'd suggest a quick trip to the dealer!

-boxster