my mark 5 has had an odd issue for some time now. my intake flap motor is bad i know that(stuck open) but i heard thats no big isssue. i get the CEL code for that every now and then. also when going WOT i will randomly get misfires, sometimes bad sometimes not so bad and sometimes accels smooth as butter. cam follower replaced, plugs n coils arent too old either. sometimes when i do a little more WOT then normal ill get a temporary CEL. sometimes flashing 10 or so times, sometimes solid for a day or so. and when that happens i get the p0402 or whatever, catalyst system effecincy below normal bank 1. ALSO this happens like cloc-work... when in higher gear under heavy load at low rpm building boost i will hear a weird wooshing noise and a slight power drop at exactly 2100rpm and last through 2300rpm then it goes right away and back to full power, that WILL NOT happen any other time except between 21-2300rpm... its not something thats just loose or anything its definatly something with moving parts or air going thorugh it. no tune or any real mods between pcv revamp and an intake. you guys think possibly clogged/bad cat? if so how can i check to be sure? and whats the best value downpipe to buy and would you reccommend heat wrapping the DP?