Help Needed with P1131 Code Ford: What’s Causing the Lean Condition?

[Nicko]

Hey all, my 2005 Ford Explorer keeps showing a P1131 code (lack of HO2S switch – sensor indicates lean). Engine seems to be running a bit rough too. Anyone else dealt with this? I’m thinking it might be the O2 sensor, but could it be something else? Do I need to replace the sensor or is there something I can do before that? Any help would be awesome!