Hello! 

I just unscrewed the oil filler cap during idle and noticed there was some pressure releasing when doing this. In all the cars i've had there was a slight suction when removing this. Although those cars where petrol cars. Is this normal for a diesel? Do I have a problem with my PCV system?

 

I have a slightly rough idle and some engine shakes. 

Edited 24 October, 20223 yr by andreasw

It's a very common thing on VAG diesels, I wouldn't worry about it.

 

It's claimed to be from excessive piston ring blow-by or a clogged/faulty PCV valve.

 

To my knowledge nobody has dealt with the issue and reported a change in behaviour and showroom-fresh cars exhibiting this behaviour suggests it is more of a design characteristic.