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Ford Aerostar engine code P0171

Got this code, possible causes are Mass Air Flow, Oxygen sensor, Ignition mis-fire, or fuel injector. Replaced the O2 sensor, have replaced plugs and wires (what a pain that was)am not interested in buying more parts in hopes they solve the problem, was wondering if anybody knows which of these problems are the most likely cause?

Don’t know for sure. It isn’t a bad O2 sensor (why did you settle on that? Not that replacing it is irrational, but it wouldn’t be most people’s first choice I think). How about a dirty MAF sensor? Or a vacuum leak?


Thank you for your most informative answer and letting me know that in your opinion I’m quite the bottom dweller in the car repair field. I’m willing to bet you are loads of fun to be with at a party.