While checking techinfo is the best place to start. This code is a fun one. I've mastered it and that'* not an easy thing to say.
Please search my username and P0171 if you want to help me out from typing it all again.
Has the LIM gasket been replaced?
Have any vacuum lines been disturbed?
Has the battery been unhooked or changed?
Once you search on the code, you'll understand better. I'm pretty sure I've written explanations to it all. Heck..I'm off to search it for you. be right back.
Here'* one P0171 and MAF
Covers a good amount.