have you checked all the turbo gaskets? make sure there is no oil leaks in the turbo..

 

Is the turbo stock? If not did it come with a regulator or did you install one? IMHO I would say 90% turbo seal. (Jeff240sx car did the same @ idle and when releasing throttle)

 

This may sound elementary, but wouldn't your plugs be oily if you were burning oil? In contrast, turbo seals leak out the exhaust side and would never show up on the plugs.

Rings would also blow a ton of oil out of the valve cover vent. Whether that is into a catch can, breather, or back to the intake, it should be easy to tell.

 

My #3 plug was coated in all sorts of nasty black shit when i blew up cyl 3, i still havent pulled the motor to see what it was that broke but most likely a bad ring since it was a 200k turbo engine