Hello,
P0171 can be set for many reasons and is hard to diagnose.
You have replaced a lot of obvious parts already, all of which can cause P0171 to set.
The first step would be to smoke test the intake and fuel tank EVAP system for leaks.
Smoke testing is a quick way to check if any of the intake or vacuum pipes have a potential air leak.
Small air leaks in either the intake or EVAP system can cause this code to set
Item like the EVAP lines from the fuel tank, activated charcoal filter or even the fuel filler cap can leak and could cause this code to set
Smoke testers are freely available online or even Amazon.
See picture below
How to check vacuum leaks using smoke and other methods.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
Leaks in the crank case ventilation system can cause this code to set.
You already have replaced the PCV valve. With a smoke tester you could induce smoke into the crank case system and check if the oil filler cap or even the valve cover gasket are possibly at fault.
A good guide on possible issues is on the below link.
https://youtu.be/xeoalEoygGg
How to smoke test.
https://youtu.be/kZsqEfP-5zM
Please let us know how you get along.
Cheers, Boris
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Monday, January 24th, 2022 AT 7:11 AM