So just throwing this on here in the hopes that someone will use the search function and find their answer

My jeep was pulling code P0131 and P0171.
My mileage significantly dropped to about 4-6mpg, black "soot" blowing out of the muffler and smell of raw unburned fuel.

I read about many different possible issues.

I decided to troubleshoot the O2 sensors first. Went over to my buddies house. Used his code reader to clear the codes. Removed my o2 sensor from the downpipe and swapped it out with his good one.
Drove the jeep and problem fixed. No check engine light. Smooth idle and obvious smell of unburned fuel gone.

Drove back to his house, and reinstalled my old o2 sensor so he could have his good one back.
While I was test driving my jeep he cleaned my o2 sensor with brake cleaner. Removed a bunch of built up crud and soot.
I reinstalled my original (cleaned) o2 sensor and have driven 1 day and about 100 miles and the jeep is doing great. Back to normal.

(Please excuse me while I knock on wood)

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