The first thing I'd check is the crankcase pressure relief valve (PCV) these are sprung loaded and are only meant to 'burp' excess pressure every now and then. The exiting gas is piped back to the inlet , however should the valve stick open then the engine tends to suck the air out of the crankcase all the time and this carrys oil over with it.
If you remove the air intake pipe and look inside where the crankcase breather is plumbed in you may find evidence of oil.
If you do find oil replace the valve.
You don't mention what engine this is but if its trubocharged then check inside the intake just after the turbo for any signs of oil as this would be an indication that the turbo oil seal is starting to fail and a replacement / rebuilt turbo may well be required. Have a feel of the turbine wheel - there should be no play radially at all - but a little bit of axial / end to end float is normal
an engine flush may also help if you've got a sticking oil scraper ring so its worth a go, as for the oil if you go up a grade / use slightly thicker oil then this is less readily drawn into gaps and less likely to be burnt off
This block as far as I can detect does not have such a v/v only a rocker cover breather feeding into the air intake through a tee piece with a reduction orifice which enters the intake on the engine side of the butterfly v/v in the throttle body, this orifice I found to be plugged solid though now cleared and oil changed to a higher viscosity the problem of smoke and miss firing remains.
The engine in question as a 1.6 8v normally aspirated unit driving through an auto-transmission ,I think from memory the engine is an AHL model. Sorry I have been so long in getting back to you I have had some family matters to deal with.