do you have the correct calibrated mass air, and do you have the idle air control valve"spacer" it goes between the iac and the egr plate and has two allen screws that you turn in and out and it will correct surging idles, and some driveability problems, you can order this spacer from your local ford dealership for 15-18$ if you already have all this i would say a vaccum leak. hope that helps
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