Dang, got 109K miles, replaced the PCV and hose back at 60K miles when I got the P0171 P0172 codes, fixed it. So now I get the P0171 all by itself, WTF? Just replaced the drivers side(easy side) valve cover gaskets, so I figured I left something off, nope everything looked good....Next looked at the PCV valve hose at the throttle body,,,,,,,looks ok, a little soft maybe, no tears,,,ok follow it back behind the engine,,,,hmmmm looks ok,,,,a little dark back there,,the boot looks normal,,,,give it a light tug,,,,holy smokes! its rotted in half! split almost in two,,,,,ok, so I pull it off and look closely, wow, the heat just fries that rubber boot,,,,replaced the PCV line and boot 15 minutes, problem fixed. :D