My Mountaineer was idling rough and sometimes stalled out when I pressed on the gas pedal to speed up. We replaced plugs, wires put an additive in the gas to get rid of any water. It ran and idled smooth right after then this evening when I was coming home from work it stared the same thing again. We were thinking fuel filter? but not sure and do not know how to change it? I appreciate any thoughts you would share with me. Thanks!