I got the codes p0171 and p0174 on my 03 5.4 Supercharged Harley. I had no drivability issues at all but after cleaning my MAF the codes came back. SOLUTION: I didn't hear any hissing but went ahead and followed the PCV hose that goes to the back center of the engine and removed the
90 degree rubber the connects to the block and it was indeed colapsed. It is very hard to get to especially if u have large arms you may need the assistance of a skinny helper. I did use a spark plug wire boot and it seems to work well................. I just wanted to share this info because after many hours of research I could not find anything for the supercharged engines. I hope I can at least help one person and save them a few $ and alot of headaches. Thanks for listening!