The engine would start but not continue running. Would do this several times

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Would have to put it in park and turn key totally off. Had the fuel filter replaced, tune up w/ new plugs,wires ect. Started better, but still has a miss and terrible fuel mileage. Have had several 454's so know about low mileage, but this is bad. It had a fuel pump indicator code at first, replaced relay on wheel well, code went away. This time no codes for bad idle.