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Code P0171

4K views 11 replies 8 participants last post by  SchwarzeEwigkt 
#1 · (Edited)
Hello there,

So, I've got P0171, car runs very well when cool but once it warms up it does lack a bit of power. Rough idle is almost non-existant, if I stare long enough it might move a hair if any over a period of a minute.

Quick background that might help:
- Recently installed new vanos seals which greatly livened up my car's driving capabilities. Not soon after that I got two codes P0491 and P0492, I quickly realized that I had torn the vacuum hose that connects to the secondary air pump. No problem, got some new hoses on both ends, then drove 500-600-ish miles all the way through part of Canada and back into the US. It wasn't until right when I hit U.S. border patrol that I got a CEL and P0174 (Carly adapter (INPA almost) states "Lean Deviation Banks 1 & 2). Now, I cleared the codes and drove just a few miles (just after border patrol) before the CEL came back, but this time I got P0171 and it's staying in Pending codes (not stored) as of right now.

Didn't have much time to really look things over today, but I did notice my O2 sensor wires (on the exhaust side by the headers) were hanging down and I had read online that they might have overheated. I've readjusted them back into place and will see if it gets any better.

I've rebuilt the DISA a year ago, new MAF two years ago, all intake boots look good, clean TB, clean ICV, new VCG (700 miles ago), fuel filter 3 years ago, all other vacuum hoses look good, F-connector is good, CCV is coming up on 2 years old now)

EDIT: The O2 sensors that I had noted were hanging down were replaced a year ago and I hadn't noticed any plastic melting, so unless it can be damaged other ways I'm sure they'd be good.

Any ideas on what else this might be?

Thank you!
 
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#3 · (Edited)
Thank you for the reply. Yeah, I've been starting to wonder if the other side of the secondary air pump hose came off of the back of the intake manifold, seemed to go on suspiciously easily when I first reinstalled it with the new hose.

Will perform a smoke test and keep this page updated.

Thank you.
 
#4 ·
P0171 and 174 are the most commonly found codes, usually due to some type of vacuum leak. The suggested smoke test is the most definitive way to pin it down. :thumbup:
 
#6 · (Edited)
Quick update:

For some reason I turned on my car and now I have the transmission COG light, car barely moves in gear at all, code P0032, ABS light, BRAKE light, CEL... but thankfully no P0171 or P0174 I guess.

I was about to have it smoke tested too like everyone had suggested but I think there's something else wrong now. ***x1f61e;

ÉDIT: I had my transmission replaced a hair under 2 years ago, so unless these are known to die this quickly I***8217;m sure the problem is unrelated(or maybe just a cable came loose).

Any ideas? Thank you guys.
 
#8 · (Edited)
Ok. I'm wondering if I can swap in my old pre-cat 02 sensors to see if the problem goes away. Can't work on my car until Monday, so again, I'll keep this page updated.

EDIT: Thought I had read codes for the transmission but it was for something else, will have to have a dealer check them then, though my Carly BMW adapter reads zero codes for the transmission.

Thank you everyone.
 
#11 ·
check the freeze frame data for the rpm the dtc set at. if it set near idle speed..it could be a vacuum leak. if its set at 2000rpm or higher...its probably a fuel supply problem. Vacuum leaks disappear at high rpm due to the drop in vacuum in the manifold when the throttle opens.

check the live fuel trim....if its +/-10% at idle you don't have a vacuum leak. if its adding mt 10% at idle and within 10% at 2500 rpm...its a vacuum leak.

if its adding at idle and 2500 rpm...you may have a fuel supply problem causing the lean condition; check the fuel pressure.
 
#12 ·
I’ve got my car apart right now chasing a vacuum leak causing lean codes. So far I’ve identified a cracked vacuum cap on the back of the engine as the only issue. All my hoses are in good shape except the little piece of vacuum line that bridges the F-connector to the plastic hardline that runs to the fuel pressure regulator on the fuel filter. It’s a bit crispy, so I’ll replace it. That and my DISA seemed a little easier to pull out than was implied, so I’m going to throw a new GAS O-ring on it too.

TL;DR: check those stupid little vacuum caps!


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