Crank case vent valve

[RichardSEL]

Hello...

Have a BWA engine 3c0 2l tFSI 48,000 mile. Have noticed that there's a lot of suction when I remove the
oil filler cap at unscrewing. And when I remove the cap with engine in idle, engine revs die down and
starts to fire lumpy. Replace cap and tick over is back to normal.

Does this indicate a failing crankcase vent valve? Or is this normal?
Had a search around the forums and the few posts with this engine and fault all speak of being unable to remove their oil filler cap due to the suction and
faults showing up on Vag-Com and a light on the dash. Don't want to get to that stage!

Any experiences or more informed knowledge would be welcome

RichardSEL

[-M-]

Sounds like everything is working fine - the crankcase vent valve only opens when crankcase pressure builds up. If the valve were faulty it would remain partially open etc and cause rough idle and running issues.

Because the engine is totally sealed when you take the oil cap off you have introduced an air leak and it will run rough.