Hesitation/Loss of Power

I have a 2001 Windstar. I have had problems with the van running rough, loss of power and backfiring. About a month ago, we changed the plugs, wires and filters. The problem cleared up after driving the tune-up, driving a few miles and putting a better octane gas in. The problems are back...does anyone have any suggestions?

Look at the ignition coil condition, behind top of the engine on the passenger side; chances are big that you will find a few cracks on it causing misfire, hesitation etc.

Are you getting any codes yet? Hopefully it's your coil because there are other more involved avenues that you may have to go down. Have you had the isolator bolt repair done? You may have build up in the EGR ports. Fuel system. Definitely check for vacuum leaks. I'd expect that you would have lean fuel codes if it is fuel or vacuum. related