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MurderousPandas · 07-24-2023, 08:52 PM

So i originally posted to Facebook, but i know the forums are a bit smarter. That and this information may help someone else. Anyway, what i got:

Need some help with a P0171 / lean code.

2013 with 190k miles. NA, decent amount of mods, but nothing new in the past few years, so issue is not mod related. Had this thing since new.

Rough idle, drives relatively fine otherwise. LTFT is near 40 at idle. Abnormal smell of fuel at idle, seems it's adding fuel that's not needed, leading me to think it's falsely reading lean and trying to correct. Fuel system seems fine, it's dumping extra fuel at idle and able to handle higher RPM fine, more likely exhaust / vacuum related. Checked vacuum lines, including that sneaky one under the intake manifold, all seem good. Exhaust has no leaks / cracks. MAF sensor clean, figured i'd check intake filter while i'm at it though likely not related, also clean. Cables are good for MAF sensor and upstream O2 sensor, no signs of damage.

Only two things i can think of are either bad upstream O2 sensor or maybe bad fuel. I did get fuel from a gas station i don't usually go to, a 7/11, before the issue began to arise, hard to believe the one time i did get fuel there it would be bad, and it's 7/11, not some super sketchy place that would buy some black market fuel or whatever. Upstream O2 has been there since new.

Only past issue i had before was a single coilpack going bad, front passenger side, likely due to added heat from modified exhaust, that was about 6 or 7 years ago.

I have a new upstream O2 sensor on the way along with a new MAF sensor because why not. Was going to drive / burn as much of this tank as possible and refuel at a more reputable gas station to check off that potential cause. Anyone have any other ideas / possibilities?

UPDATE: fuel from Shell seems to run much better, but still high LTFT. Moral of that story: fudge (this particular) 7/11. Logs show O2S2 reading 0 volts, mixed messages in forums about it always reading 0, but i'll zero out A/F #3 in Romraider to see if that helps. So maybe bad downstream O2, though no idea why it'd affect fueling as it's primary purpose is to monitor cats.

07-24-2023, 08:52 PM	#1
MurderousPandas Senior Member Join Date: Jun 2015 Drives: 2013 Scion FRS Location: Key Largo Posts: 331 Thanks: 20 Thanked 118 Times in 80 Posts Mentioned: 3 Post(s)	P0171 (lean), possible false reading So i originally posted to Facebook, but i know the forums are a bit smarter. That and this information may help someone else. Anyway, what i got: Need some help with a P0171 / lean code. 2013 with 190k miles. NA, decent amount of mods, but nothing new in the past few years, so issue is not mod related. Had this thing since new. Rough idle, drives relatively fine otherwise. LTFT is near 40 at idle. Abnormal smell of fuel at idle, seems it's adding fuel that's not needed, leading me to think it's falsely reading lean and trying to correct. Fuel system seems fine, it's dumping extra fuel at idle and able to handle higher RPM fine, more likely exhaust / vacuum related. Checked vacuum lines, including that sneaky one under the intake manifold, all seem good. Exhaust has no leaks / cracks. MAF sensor clean, figured i'd check intake filter while i'm at it though likely not related, also clean. Cables are good for MAF sensor and upstream O2 sensor, no signs of damage. Only two things i can think of are either bad upstream O2 sensor or maybe bad fuel. I did get fuel from a gas station i don't usually go to, a 7/11, before the issue began to arise, hard to believe the one time i did get fuel there it would be bad, and it's 7/11, not some super sketchy place that would buy some black market fuel or whatever. Upstream O2 has been there since new. Only past issue i had before was a single coilpack going bad, front passenger side, likely due to added heat from modified exhaust, that was about 6 or 7 years ago. I have a new upstream O2 sensor on the way along with a new MAF sensor because why not. Was going to drive / burn as much of this tank as possible and refuel at a more reputable gas station to check off that potential cause. Anyone have any other ideas / possibilities? UPDATE: fuel from Shell seems to run much better, but still high LTFT. Moral of that story: fudge (this particular) 7/11. Logs show O2S2 reading 0 volts, mixed messages in forums about it always reading 0, but i'll zero out A/F #3 in Romraider to see if that helps. So maybe bad downstream O2, though no idea why it'd affect fueling as it's primary purpose is to monitor cats.