Long story short, I have the aFe Takeda Cold Air Intake. Plugged the intake valve and had a breather venting to atmosphere which ended up causing the P0174 code and causing positive short and long fuel trims at idle.

Everything was driving good for about 5 months, no check engine light nothing through out winter. Fast forward to late April, check engine light was appearing with codes P1071 & P0174, replaced gas cap, cleaned MAF sensor, checked for any cracked/loose hoses and erased codes.


Few days later they reappeared, but this time i get P0171, P0174 and P0456. Recheck gas cap, retighten, check MAF sensor unplugged it while the car was on readings indicate MAF sensor was working fine. And clear codes.

Now about 4 days later, codes reappear but this time only P0174… again recheck all hose lines, unplugged, replugged and reinstalled MAF sensor...
Decided to finally just look at the live data, everything was looking normal besides the long and short fuel trims with long fuel trim 2 showing a positive 25 and fluctuating down to 18-19.

Read somewhere that plugging the vent valve from the intake increases the positive fuel trim and gave it a shot.

Removed the breather and replugged the vent valve cover tube to intake, restarted the car, plugged obd2 in and saw the fuel trims go back down to -2 to 0 to postive 2 and bam CEL GONE!

this drove me into a rabbit hole nearly wanting to spend money to replace all o2 sensors, look at the fuel pump/filter etc. but luckily it was a simple fix for me.