How do I fix code P0171?

Question

Keeps setting code. When deleted first key cycle sets pending. Second sets code. The vacuum lines connected to intake (purge valve, pcv valve, brake booster) were removed one at a time from the intake and plugged off. Short term fuel trim (stft) did not peg negative to bring down the long term fuel trim (ltft). Thus isolating each system and eliminating it for possible leaks. Sprayed carb cleaner around intake and could not cause stft to peg positive. Visibly checked intake snorkel and breather lines. No leaks seen. Changed spark plugs. No change. Forced lean then rich to check upstream o2 sensor. Pegged 0 then .98 volts on a 0-1 volt graph. Good o2 sensor. Disconnected battery then rechecked fuel trims. Immediately jumped to 28% ltft within less than I minute meaning issue is at idle. Can't hear an exhaust leak. And unplugged map sensor which only caused stft to go 10% positive. Running out of ideas. Possible fuel? Any suggestions?