The crankcase breather of the five-cylinder 2.5 TFSI leads the oil vapour into the intake, and the stub of the diverter valve sits directly next to it. When the diverter valve opens on lifting off, it carries the oil vapour along, and the vapour condenses in the air filter housing, because the stub is right in front of the housing. The oil therefore collects on the filter element and in the bottom of the housing, the amount grows with use, and under load oil mist comes out of the intake pipe as well. The consequence is twofold: measurable oil consumption, and oil reaching the intake speeds up the carbon build-up on the intake valves, which is already heavy here because of the direct injection. This is not a broken part but where the line runs, so it shows up around 40,000 km already, and earlier on a car used hard. The repair is rerouting the breather or fitting a catch can, 200 to 600 euro.
What to check
- Take the air filter housing lid off and look at the filter element and the bottom of the housing
- Wipe the inside of the intake pipe with a finger: an oily film belongs here
- Ask whether a catch can has been fitted or the breather has been rerouted
