Good morning,

I have a 2003 F150 4x4 Lariat with the 5.4L. The truck has just under 200K miles on it. Recently I have had a P0171 and P0174 codes (engine lean codes) appear. I initially assumed it was a vacuum leak, so I examined all my vacuum lines, tried spraying carb cleaner on the lines, intake etc. No luck, finally made a smoke machine and tested for any vacuum leaks. No vacuum leaks found. After driving around for about a week, a new code appeared (O2 sensor, P1131).I then took it into the local shop for further diagnoses. I was told it needed a MAF sensor, and my fuel pressure was on the low side. I understood both of these issues could cause a lean code, I then replaced both of these myself with motor craft parts. Cleared all codes and drove the truck. To no avail, the codes have come back, now I have 4 codes, P0171, P0174 (lean codes), P1131, P1151(upstream heated O2 sensors). The O2 sensors codes do not show up right away but later on after driving about a 100 miles or so. These codes have been here for about two weeks now, and within these two weeks, the truck will stall at idle. Does not stall when cold, only when truck reaches operating temperature. Truck will stall all the time when stopped (never when moving). I have scheduled to take it in to the local Ford dealer for diagnosing, however looking to solve this myself. My question(s), would faulty O2 sensors cause lean codes? If yes, then why do the O2 sensor codes appear later and not right away? Could faulty O2 sensors cause the vehicle to stall? Where else should I look for?

So when the codes came back, take a look at the freeze fram data.

More than likely it was the P0171/174 that tripped the light and the P1131/1151 are just collateral damage.
So first solve the 171/174 issue. It is possible that low fuel pressure or a dirty MAP sensor could cause it to run lean.
But did you verify the fuel pressure with a gauge? What was the pressure?
Has the fuel filter been changed?

And you double checked the infamous vacuum elbow between the intake manifold and the firewall?
(Since the idle is computer controlled, when you spray carb cleaner the IAC reacts too quickly to hear a change in idle. But if you are monitoring the fuel trims while spraying you may be able to SEE the change.)
When you smoked it did you check for smoke back by the charcoal canister Incase the purge valve was leaking?

Any exhaust manifold leaks?

Stick with it. Hope you narrow it down!