I currently have a P0420 code which ive read is commonly associated with a failing cat. I also i think I'm starting to see the purge valve going bad, it's been idling a little rough and this last fill up it started surging at idle. I read that the purge valve can also cause a P0420 code. So maybe my cat is still fine for now. One other issue that has started happening is my boost pressure surges at low boost, if im lightly accelerating and getting up to 4-5lbs of boost it starts dropping down to 1 lb and surges back up to 5. I did have a charge pipe blow off not long ago, could it be a boost leak or could the purge valve cause boost to fluctuate like that?