I would like to share my experience on how I finally fixed my PO305, 171 and 174 on my 1998 F150 V-6, 4.2 with 215,000 miles. First I could have NOT done this without the technical knowledge of "Bluegrass" and "Jbrew". These guys know their stuff. I have read many of their post on here and I took bits from all their post and used it to help me. Don't be afraid to ask these guys any questions cause they are very helpful. Just don't be a blockhead like some are and do the opposite of what they tell you.
My luck was not so good as I had more then one problem happening at once. After changing the common things (wire, plugs, fuel filter and coil pack) and doing test on everything possible, I had to remove the plenum to fix the problem. Found that all my ports were clogged. I have seen old BBQ grills that were in better condition then my intake After removing the plenum I also found dry rotted, brittle vaccum lines and connectors. Found bad PCV also. Since everything was exposed, I figured why not replace all while I can, so I did. After a couple of hours and a few beers I got the plenum and intake looking real good like new. Using my air compressor was fun blowing out all the carbon deposits for the egr ports. Put everything back together, fire her up and she ran like new. Took her out for a short and easy ride and so far no CEL. Hopefully tomorrow I will take a longer ride and see what happens

 

good deal