R53 Blow By from oil cap
 

so i started up my car today and noticed it was sounding a little rough. so i immediately shut it down and popped the hood. i didnt notice anything wrong so i restarted it and it was sounding normal. i then decided to check the oil cap to see if there was blow by and there was a large amount of blow by.

i have a 17% reduction pulley, cat-back exhaust, cai, and msd coil pack with iridium spark plugs. i have notice a small misfire that has never thrown a code. i believe it is because i am still on stock fuel injectors.

so my question is, what would cause the blow by other than the typical things such as piston rings, or cracked piston?

any help is appreciated.
thanks