It sounds like you have more than one thing going on.
First, the color of the smoke: if its gray, it could be water. How does your oil look?
Milky? Oil in water is cracked block, cracked head or blown head gasket.
Second, the flicker on you vacuum test could be a stuck valve. I would guess it would not like to idle lower than what you have.
These two together would give you your symptoms.
As Caso says a compression and leak down will give you more info.
Good luck. Hope this helps. Let us know as you go along.
Mark
