Regardless of what it is, it is the classic sign of a leak...I wouldn't have done the tune until all modding is done...anyway...I would do as suggested above...or, just take everything back off, check the gasket, check fitment, put it back on..but something didn't line up or seal for sure, also look at all you hose connections, even the one's you thought you didn't touch,,lol...Good luck with it...