Don't forget the coil pack
I'd like to add to the P0171/P0174 issue. I too got these codes, along with P0303. Rough running under acceleration, but not at idle. Did all the isolator bolt gaskets, cleaned MAF, checked EGR, checked plugs, looked for vacuum leaks. Nothing helped until I removed the coil for inspection. Others have said cracks develop in the epoxy on the underside of the coil, but I found cracks had appeared at the base of the coil towers. I initially just cleaned the coil thoroughly and the engine now runs perfectly. Obviously this will need to be replaced, but just wanted to add my experience.
Thanks to all on this sight for the help.