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P0171 & p0174

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Old 05-20-2013, 04:28 PM   #1
Vic'sVette
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Fuel trim system lean bank 1 & 2.

2001 coupe, a4, 100k miles, pretty much stock under the hood. Swiss cheesed intake (did idle relearn procedure), new plugs & wires, new fuel filter, cleaned MAF sensor, techron fuel treatment, still intermittent check engine light. Not throwing any DIC codes.

Check engine light started coming & going intermittently a few months ago. That's when I started replacing stuff that I knew needed replacing anyway (plugs, wires, fuel filter).

Started with p0171, but since it's now p0174 also, I don't think its o2 sensor, unless it's 2 or more of them.

Any suggestions????
Thx
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Old 05-20-2013, 05:47 PM   #2
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Originally Posted by Vic'sVette View Post
Fuel trim system lean bank 1 & 2.

2001 coupe, a4, 100k miles, pretty much stock under the hood. Swiss cheesed intake (did idle relearn procedure), new plugs & wires, new fuel filter, cleaned MAF sensor, techron fuel treatment, still intermittent check engine light. Not throwing any DIC codes.

Check engine light started coming & going intermittently a few months ago. That's when I started replacing stuff that I knew needed replacing anyway (plugs, wires, fuel filter).

Started with p0171, but since it's now p0174 also, I don't think its o2 sensor, unless it's 2 or more of them.

Any suggestions????
Thx
Check your pvc hoses and connections. Not uncommon for these to develop cracks and holes which can set lean codes.
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Old 05-20-2013, 11:27 PM   #3
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Check your pvc hoses and connections. Not uncommon for these to develop cracks and holes which can set lean codes.
vacuum leaks will cause your codes. Also check your intake to head seals! Use some carb cleaner and spray around the intake while running. You will hear a change in rpm when you spray in the area of the leak! Good luck!
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Old 05-21-2013, 12:54 AM   #4
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Check your pvc hoses and connections. Not uncommon for these to develop cracks and holes which can set lean codes.
Also check for leaks AFTER the MAF. ie loose clamps, cracks in the rubber connections and/or air bridge. With 100K the PCV lines are probably the most likely suspects.
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Old 05-21-2013, 01:05 PM   #5
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Thx for the help. I'll check those pcv lines first, & go from there. Crappy weather outside, so good day to work on it instead of driving it...

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Old 05-22-2013, 09:49 AM   #6
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My 2000 coupe had the same codes, tracked it to the pvc line which had deterioted over time. Changed the line and pvc and now she runs great.
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Old 05-22-2013, 10:38 PM   #7
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If you don't find any vacuum leaks, have the freeze frame data checked. This will tell you the exact contains when the codes set. If its not at idle speed with closed throttle, you probably have a skewed MAF sensor.
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