Lean condition - only shows P0171 code

[tjfreeman1911]

Howdy,
I'm fighting a lean code on my 2001 explorer xlt 4.0L v6 SOHC. The reader only shows p0171. I've cleaned the MAF sensor 3 times so far and changed the air filter. I had a K&N in there and I read the oil on them can keep mucking with the MAF. Now it's got a paper STP filter in it.
After I clean the MAF it rides better for a while then gets worse as time goes on. I also replaced the entire PCV assembly and the spark plugs and wires. I bought upper and lower intake manifold gaskets, but haven't installed them yet, but they are on-deck if something else doesn't come up.
I read the OBD-II page for DTC P0171 but wanted to reach out to the forum and see what y'all think.
Thanks!

 

[Vic_Ferrari2002]

Don't forget to check your vacuum hoses for leaks. That will also cause lean conditions. A good scanner will tell you what the fuel trims are and help you narrow down what is causing your lean condition.

-keith