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Reads out a P0171 , when system at normal temp, will NOT IDLE.
Changed O2 sensor. It did help a little, will idle with a little roughness once and a while.
Off idle everything is fine. I'm thinking the MAF sensor is dropping out at the low end?

Vehicle: 2005 Ford Focus ZXW 2.0L Manual trans

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I agree. You should start by cleaning the MAF sensor, the O2 sensor shouldn't cause any driveability problems.
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I have tried cleaning the MAF, no help. I bit the bullet and replaced it.
Again, NO HELP. Must add, so far the upstream O2, MAF sensors replaced, replaced the inline fuel filter for peace of mind. I'm left with possible fuel pressure problems (I have no way of checking that!) of injectors.
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P0171 Ford Code - Fuel Injection System Too Lean Bank 1
Read more: https://www.autocodes.com/p0171_ford.html

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