What is codepo171 174

I had these codes on my F150 several years ago along with several other codes that really turned out to be false codes and it was the PCV vacuum hose that connects to the PCV valve in the valve cover(4.6L).I really could not here it leaking,BUT it was covered with foam insulation so 1st thing I cut that insulation back a little,THEN that hose (bout 3" long)was collapsed flat/split turned to mush! I replaced that hose and all codes went away.check ALL your vacuum hoses for leaks.the one that goes into the top of the intake manifold at rear of engine(elbow) bad to leak there also,carb cleaner comes in handy finding leaks,but be careful when using this,if no vacuum leaks from hoses or intake manifold,then try cleaning your MAF Sensor carefully with CRC MAF Cleaner ONLY>Part Number: 05110.there are other things it could be,but try above first.I'm sending you a link,more detailed if you can't find the problem.copy and paste the link below,good luck! http://troubleshootmyvehicle.com/ford/4.6L-5.4L/troubleshooting-p0171-and-p0174-page-1