Question about 1999 Mercury Cougar

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Running Rough: P1131 & P0171 DTCs

Hey :) I have a 1999 Mercury Cougar that is running rough. I ran a diagnostics on it and came up with two codes: P1131 & P0171. I am wondering what the likely cause of these DTCs may be and how to fix this at home. I am guessing it is something to do with the O2 sensors?! Thanks so much, any help is appreciated! (Oh, also, I had new spark plugs and wiring done, which did not solve the problem.)

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  • divinity_83 May 31, 2009

    Thank you! Where about is the MAF sensor located? I will definately try this first!!

  • divinity_83 May 31, 2009

    Thank you! I cleaned the MAF, and now the check engine light is gone and it's running smoothly!! You are fantastic, I truly appreciate your help, you saved me a trip to the mechanics! $6 bottle of cleaner and a security screwdriver bit and the problem was solved :)

  • divinity_83 Jun 01, 2009

    LOL< well now you may hate, I took it out on the road, running MUCH better however still hesitant/rough when first accelerating from stop, check engine flashed at me once or twice for 1-2 seconds. I ran another diagnostics........Now I have P0306 (Cylinder 6 Misfire detected) and a P0300 (Random Misfire detected). Doesn't really make sense as 6 months ago I had all the spark plugs and wiring what?? :) Thanks again!!

  • divinity_83 Jun 02, 2009

    w00t, fixed it again. I figured I'd check out the spark plugs, spark plug in #6 was loose from the's running fast and smooth now! Thanks again!


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They both refer to oxygen sensors, but a lot of times a dirty mass airflow sensor is the cause. Get a can of Tuner cleaner spray from electronics store, or radio shack & remove battery cable (Neg - ), then remove MAF sensor and clean it well with the spray & let it sit & dry out for 1/2hr or so, then re-install & try it. Careful with the wires, they break easy. I don't recommend carb or brake cleaner be used, because they leave residue, which kinds of defeats the purpose of cleaning it.

Posted on May 31, 2009

  • Mike Butler
    Mike Butler May 31, 2009

    Your welcome, glad to help ! "Happy Motoring"

  • Mike Butler
    Mike Butler Jun 01, 2009

    Might be time to have fuel pressure tested. If it's low, it may be starving fuel system, thus injectors don't supply enough or any fuel, thus misfire detected. May just need new fuel filter too.


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