Most likely your problem is your IAC valve. These will cause sputtering, sluggish idle, extremely high idle when first starting up, and also could cause the car to die after being cranked. You can get IACs a lot cheaper than you used to...less than $80 bucks all day long at NAPA.
But just for kicks, disconnect your positive battery cable first for about 20 minutes or so to allow the computer to reset itself. I've seen it cure everything from check engine lights to rough running.
2000 Mercury Grand Marquis GS