Just like Corey (njdaewoo) who posted back on 3 June I have a 2001 Windstar that had the same exact symptoms. After changing virtually all the sensors and the plugs/wires (to get the back 3 plugs the cowl MUST come off - it gives plenty of clearance) it still had a rough idle and misfiring.
I then changed the COIL PACK and the problem cleared up! The Windstar runs like a scared rabbit. My problems also started right after I put in some cheapo gas.
Change your coil pack (the black plastic piece where all the plug wires plug into in the back) and then report what happened next.
I also did the procedures described here below and it didn't help me at all. You're welcome to try but I would say change the coil pack FIRST. These are kinda long:
2000 Ford Windstar (Codes 171 and 174) 2000 Ford Windstar (Idel Air Control Problem)
GOOD LUCK and let us know!
Gonzo
Westland, Michigan
