Mercury Mystique

I have 98 merc mystique, a week ago I started having a hesitation in acceleratio, it has gotten worse and now the engine light has com on. The car has 124000 miles, it has new spark plugs, is in good shape. AC went out after I bought it, the ac pulley has been bypassed with a different belt. It was great until this. Please help
June 9, 2007.

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