I have the same problem with the car mainly on decel and sometimes during idle. Ive broken it down to these
Valve stem seals Turbo needing rebuilt
Worn piston seals
Thin oil
PCV valve
I started with changing the PCV and i can now decelerate without any smoke or idle. But I still do get a bit of smoke when I load it up my driveway slowly. Start with the simple things first. If i disconnect my breather hose to the turbo intake i dont get any smoke from the exhaust.
With the idle problem did you clean out your TB, there is some rubber stuff that helps it to seal and people usually scrub it off and the car wont idle well. The rubber stuff tends to look like carbon build up aswell.