I have installed a performance air kit K&N intake on my Skoda Octavia 2.0tdi PD 140bhp 2009. Is the vacuum pipe on the old air filter box necessary to install a nipple on the new intake pipe? Or is it necessary to block the pipe with screw? What are these vacuums for?

Follow it to see what it goes to at the other end?

One thing's for sure, it's a source of filtered fresh air, not vacuum, for something, if coming from the airbox.

Leave it disconnected but open.

Normally a pipe from the air filter etc is a breather pipe or similar so should probably be left open.

Alasdair

Might be worth creating a small gauze filter or similar if its been left open just in case something goes down it.

Alasdair