I can guess , but when changing my PCV valve, I noticed a (steel or brass tube) it was night, inline with the PCV. one side had an inlet like when you put air into your tire, the other just an opening. I can guess it is to keep boost from leaking or entering. I think I put it in backwards because now the car seems to surge at low rpms. Hmmmm I will try to turn it around and see if that is what is causing it but does anyone else use this? This has been on the car since I bought it and never noticed it.