Either a turbocharger seal is leaking or there’s a crankcase ventilation problem would be my guesses and a clossed converter is also a possibility.
The easiest way to check for a clogged converter would be to use a vacuum gauge. Those gauges are cheap to purchase and very easy to use. A new gauge should come with an instruction sheet showing how to interpret gauge readings.
When it comes to clogged exhaust the gauge can exhibit several different readings although the instruction sheets only show one.
The odd one out is to rev the engine quickly at idle and let off. The needle should drop instantly to zero and then return to a higher than normal at-idle reading. The needle will then drop off slowly to the normal at-idle reading.
This is all assuming there are no vacuum leaks and the engine is sound mechanically.
The gauge will also show you instantly if there’s a mechanical problem with the engine itself. Hope that helps and good luck.