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Q: rough idle on 2005 Mercury Monterey

Our van has been running rough and misfiring for about a week. We have had the spark plugs and wires replaced as well as the catalytic converters. Each repair corrected the problem for only about a day. The check engine light is on again now, and the previous error has been "cylinder 1 misfire". What could be the problem now? Could gas with ethanol cause this problem?
Thank you!!
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The question I would have is: What are the failure codes now? If you are still sitting with a cylinder 1 misfire issue, you may want to look at the fuel injector on the affected cylinder for problems. Why did the Catalytic Converters get replaced?

Ethanol is supposed to be used only on Flex Fuel vehicles, unless it's used as mixed nominally with conventional fuel at the refinery. I do not believe your Monterey is Flex Fuel capable.
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