I have a 1.6 TDCi focus c-max and have recently had issues with power fluctuations and the engine feeling lifeless.

To rectify these problems I have had the vacuum pipe that's attached to the acutuator that controls the variable vains in the turbo replaced.

Also, there was a considerable amount of oil in the air pipe that comes from the air filter which covered the MAF sensor. I cleaned the pipe with brake cleaning spray and the MAF sensor with IPA spray.

Is it normal that oil enters the air inlet pipe via the rocker cover breather pipe? If not how can it be stopped?

Thanks
Brendan