Surging idle
 

Ok I'm just going to get to the jist of it. I know this is a topic that has been beat to death on here due to my research but I'm going to ask anyway so please forgive me. A week and a half ago I had to add a litre of oil to my truck. Said truck is a 2003 F150 2WD Supercrew, 4.6 litre with 314,000 km. The truck great until this moment. I went into work that night( midnight shift), I left at 4:30 in the morning to go deer hunting( I know I'm a bad person).I let the ruck warm up for a couple of minutes before leaving when the service engine soon light came on.
I took out my code reader that is always in the truck, to find out I had both lean bank 1 &2 codes. Now it has a higher idle than normal. around 1100 rpms, but once it gets to operating temperature it drops after the truck sits, either in park or in gear, down to 550 to 600 rpms. But when it does the it sounds like it has a real agressive camshaft lopey sounding. Now I've read on here through Google about vacuum leaks. I did the propane torch test, not finding anything conclusive. I have unplugged various vacuum lines but found idle to get worse. Would it be upper oxygen sensors without a code? Camshaft sensors? I understand the vacuum plug at the back of intake is a culprit sometimes. Can this vacuum plug be purchased from Ford? Any ideas would be helpful. Thanks in advance for any help and people's patience.

Fuel pressure? Or Fuel Rail Pressure sensor? Fuel filter? The O2 sensors 'must' be working to some certain degree as THEIR reading being off (TOO LOW) is what prompts the lien code. Doubt both side O2 sensors failed together at same time. I do not know if your model has a fuel pump driver module or 'returnless' fuel system, but if your reader can give fuel pressure (relative to intake manifold vacuum), but that would be helpful diagnostic info at this point.