Code P0171 on STOCK car
 

Hello everyone!
I'm having some troubles with my completely STOCK 2018 BRZ...
Can someone help me out?

Let me sketch the situation:
Fault code P0171 appears, which means that it's running too lean according to the ECU.
Both the check engine light and traction control light are on.

This is what I have done up until this point:
- Swapped out ALL injectors
- Performed a smoke test to detect intake leaks (there were none)
- Swapped out the Oxygen sensor (nothing changed)
- Checked the MAF (was OK)
- Checked all values on SSM4 (so fuel pressure etc. are all good)
- Tried injector cleaner
- Several tanks of fuel were used in the meantime so it was not due to bad gas

The odd thing is that when I'm collecting data, I can see that the A/F sensor is telling the ECU that everything is ok, but the Oxygen sensor is telling that the engine is running too rich. So I don't get why the ECU is throwing the lean code. This is all measured while running without check engine light.

When I clear all codes and start the car, it dies and each time I start it again it struggles to keep running. After some tries, it manages to stay alive but the fuel trim levels are getting adjusted. I can smell that it's running rich and i can hear some backfires in the intake or exhaust when I'm trying to keep it alive by pushing the throttle.

I have another A/F sensor to try as well but I'm afraid that this won't fix it either...
Does anyone have experience with this fault?

Car has around 31k KM and no mods at all were done to it. Not even a sports air filter or so...

Thank you all in advance!

i had the same code and took it to subaru. turns out it was a broken valve spring.

Wasn't the valve springs issue sorted through a recall.

It's a 2018 facelift model, wasn't this solved in this generation?