Overnight with this cold weather the valve stuck open and dumped oil into your intake manifold. The reason the rpm were dipping is because the oil was smothering the engine - hence the smoke (burning oil).
Leave the car in the garage overnight or find a way to heat up the ccv plus it's lines somehow before driving it. Then drive the car REALLY hard to burn all the condensation.
You'll be alright. Btw I speak from experience. Happened to me last winter. Try avoiding short drives and drive the car hard especially in these colder weathers - this will not solve the problem but can help avoid it.
Last edited by 328iInt.o; 02-11-2012 at 05:46 PM.