Hey guys I'm back, decided to create a new thread since the last topic didn't really turn out to be my issue. So right now I'm having an issue with my 05 G35 coupe running very rich. The STFT is almost constantly at +25%.

Things I've done:
Repaired any exhaust leaks
Tested A/F sensors (B1/B2 good according to FMs)
Tested HO2 sensors (B1/B2 good according to FMs)
Used fuel additive (Gumout) to clean fuel system
-(X2 in a 3000 miles period)

Obviously still running rich since I'm here.

Things I've noticed:
At idle both banks now go into OL_Fault when the ECM tries to trim it back to 0%.
LTFT maintains +9.4%
Throttle position at idle is 3.5%

Mod list:
DC cold air intake
Cat back dual exhaust

Any help is appreciated. TIA!

First suspect for that sort of issue is always the MAF. It's the one component in the intake stream that the ECM simply needs to trust, because there's no MAP sensor on most N/I engines to cross-check it. The IAT sensor can also make an engine run crazy-rich if it reads "Siberia" all the time. Both of them will rarely cause any codes, and even when they do the ECM will usually blame something else or throw a "WTF" code like P0101.

I did the FM task to test the MAF (integrated IAT sensor) and it tested good. It was actually the topic of my previous post. Once I got that issue straightened out it came out good. I'm suspecting an A/F sensor.

Here's the interesting thing now. I got a P0171 code (bank 1 lean) and a P1283 (A/F S1/B1) but both sides run +25%

The FSM procedures are pretty much aimed at diagnosing a MAF that's flatlined, but they won't tell you if it's operational but lying. Even a before-after-IAVL comparison can only tell you if it was mis-calibrated, not if it has an unusable range or slope.

When P0171 isn't a vacuum leak, a dirty Throttle Body, or a bad PCV Valve, it's almost always a lying MAF. The P1283 is a "performance" code too, not a flatlined A/F, so it doesn't exclude much. It could also be nothing, because I don't know if you cleared the self-learning after some of your other travails. If self-learning isn't cleared then P1273/P1283 can keep coming back even though the issue has been resolved, there's a bulletin about that. So check those other things first, especially the PCV system, but if they check out, I'd throw a different MAF at it just on general principles.