P0171, bad idle, low power, stuttering
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This is a discussion on P0171, bad idle, low power, stuttering within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hi, My WRX has had some issues lately. It use to show a misfire cylinder 3 code so I changed ...

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    P0171, bad idle, low power, stuttering

    Hi,
    My WRX has had some issues lately. It use to show a misfire cylinder 3 code so I changed the spark plugs and seafoamed the intake. Now there is a P0171 - System too lean (Bank 1). It's idling really low (750 rpms), stalling when I push the clutch in, and it feels really low on power. The boost gauge says I'm at the correct psi for stage 2, and it's holding pretty well, but the car feels like it has the same power as it did when it was stock. When I accelerate with about 30% throttle, the car will be fine until about 3000-3400 RPM where it will jerk a few times and lose 50% power, then repeats this from 4000-4250 RPM. I changed my oil yesterday and there were specks of metal. It looked like flake in metallic paint so I'm sending the oil out to be analyzed. I have cleaned the IACV, the MAF, and seafoamed the fuel but nothing has made a difference. Is my engine in bad shape? Could this be a problem with my fuel system? I just need someone to point me in the right direction.

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    Registered User Replay's Avatar
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    This is a longshot... but whens the last time you changed out your fuel filter? Also, how many miles are on the car?

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    Moderator Donkey's Avatar
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    P0171
    Fuel trim malfunction (A/F too lean)

    Your car is supposed to idle at 750rpm at full warm up........
    Sounds like you maybe borked the O2 sensor.How exactly did you do the Seafoam treatment for the intake?Please don't tell me you used the brake booster line.
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    Quote Originally Posted by Replay View Post
    This is a longshot... but whens the last time you changed out your fuel filter? Also, how many miles are on the car?
    I've never changed the fuel filter in the ~40,000 miles that I've owned the car. It has 80,000 now. Could bad injectors be a suspect, too?

    Quote Originally Posted by Donkey View Post
    P0171
    Fuel trim malfunction (A/F too lean)

    Your car is supposed to idle at 750rpm at full warm up........
    Sounds like you maybe borked the O2 sensor.How exactly did you do the Seafoam treatment for the intake?Please don't tell me you used the brake booster line.
    I used the vaccuum hose off the BPV. Maybe all the carbon crud fubar'd the O2 sensor? I'm guessing it would be the front sensor (A/F).

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    Moderator Donkey's Avatar
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    Quote Originally Posted by B-RySuby View Post
    I've never changed the fuel filter in the ~40,000 miles that I've owned the car. It has 80,000 now. Could bad injectors be a suspect, too?



    I used the vaccuum hose off the BPV. Maybe all the carbon crud fubar'd the O2 sensor? I'm guessing it would be the front sensor (A/F).
    Defiantly change the fuel filter and yep front O2 sensor.You could try and just reset the ECU and see if anything changes.Remove neg battery cable,hold down brake pedal for 1 min and rehook up neg battery cable.This will wipe out all RAM and let the ECU relearn it's fuel trims.Hopefully the DTC will be cleared and the CEL will be off.
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    Quote Originally Posted by Donkey View Post
    Defiantly change the fuel filter and yep front O2 sensor.You could try and just reset the ECU and see if anything changes.Remove neg battery cable,hold down brake pedal for 1 min and rehook up neg battery cable.This will wipe out all RAM and let the ECU relearn it's fuel trims.Hopefully the DTC will be cleared and the CEL will be off.
    Thanks for the help. I'll change the filter ASAP, and find a new O2. I forgot to mention, I have an APv1, and I've reset the ECU only to have the CEL come back.

    One more question...
    I'm flashed to stage 2 with the AP but I have an AEM short ram with K&N filter (I know, I know...big shame). An aftermarket intake would definitely be leaning things out, but could it be causing the CEL and my problems?

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    Quote Originally Posted by B-RySuby View Post
    Thanks for the help. I'll change the filter ASAP, and find a new O2. I forgot to mention, I have an APv1, and I've reset the ECU only to have the CEL come back.

    One more question...
    I'm flashed to stage 2 with the AP but I have an AEM short ram with K&N filter (I know, I know...big shame). An aftermarket intake would definitely be leaning things out, but could it be causing the CEL and my problems?
    Potentially. See here:
    P0171 CEL Thread - Everything you ever wanted to know? - NASIOC
    WRX Info Links, Courtesy TheJ
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    bringing a thread back from the dead. Did you ever fix your problem? This is exactly what I have going on right now!

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    UnBanned Sinister's Avatar
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    I had this problem a couple nights ago. When a vacuum line pops off, it causes the idle to run lean. That's what throws the p0171 code. I resecured the vac hose with a hose clamp, and sure as sh1t, the thing runs like a champ again.
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    do you have an accessport? Because I can help you diagnose the problem
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    Quote Originally Posted by Sinister View Post
    do you have an accessport? Because I can help you diagnose the problem
    So maybe Ill just go crazy with hose clamps on vacuum hoses. What hose popped off on yours? and no accessport.

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    P0171, bad idle, low power, stuttering

    The return line to the manifold from the fuel evap solenoid.
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