Long shot, but I had one similar at work last week, ended up to be VERY simple. At the back of the engine, drivers side, there's a solenoid for the turbo wastegate with 3 pipes on, the pipe from the solenoid to the turbo was leaking (they have a rubber elbow into a plastic pipe, the plastic pipe was loose in the elbow) replaced the elbow and it was sorted.

Have you had the fault codes read? The MAF sensors get contaminated with oil also.