Pcv valve. Pretty comon on this motor. Have thesame problem on my Cupra.
If you feel that the car behave strange then you need to fix it. But ive been driven mine since June -14.
Mine has som kind of leek, like the valve doesnt tight all the times.
First my choice was Milltek, but read on the forum that people experienced that it was bad quality for the money and Bcs was/is better and a little bit cheaper.
Havent got one yet, need to sort the Twin exhaust valance first :).