Some may be OK, if it is excessive you could have bypass of the rings or some other compression problem. That could explain the smoke because it would be a little diesel and a little oil. That's when you might get the compression checked.
Some oil going into the intake tube from the ccv is normal so don't get worried if it's a little oil there.
There is a lot of other things it could be related to injection of fuel but when you said they cleaned the turbos and it was OK for a while that sounds like oil getting in there. So there is an oiler for the turbo or through the ccv into the intake tube or exhaust (smoking engine) / both.
Added..
You can't be too sure about the oil level. It's possible oil is being replaced by fuel. It only takes a very small amount of oil to make a lot of smoke so if it's suttle it's likely not too bad.
If all else is good maybe injector problem.
Last edited by DavidPhillips : 07-08-2009 at 05:25 PM.