99 frd expl 4.0L codes p0171/0174

just a quick note. Had these codes off and on for a while. read all posts and checked everything possible and listed, from maf to intake leaks to fuel pressure. Erased codes and back they came again and again. Nothing worked. I was under my truck a few weeks ago changing the oil when I noticed the fuel filter. That was the only thing I didn't think of so I replaced it. Filthy! CEL hasn't come on since I cleared the codes (3 wks and counting)with my scanner, Truck is running great and getting better gas milage. Thought this might help

-jumante