Miss/Surge - found the problem
I have a 1999 Taurus with a Duratec. It had a miss/surge that was intermitent and most evident when accelerating or sitting idling in drive, it was worse when the AC was on. The engine light didn't come on.
The car has 100,000 km (60,000 miles) and has always been very well maintained. The plugs and wires were changed about 2 years ago, Autolite Platinum, and Bosch Wires.
I cleaned the IAC and it seemed to help a little but didn't cure the problem.
I pulled the upper intake and the plugs. On one of the plugs I noted a visible voltage leak (track) running down the insulator. The plug was shorting out to ground. I checked the wires and they were fine. I purchased new plugs and coated the insulators and the inside of the plug boots with a light coat of dielectric (insulating) grease. I just put it on the boots and insulator, not on any electical connections.
The car runs like a champ, I'm almost sorry that I ordered a new Fusion Sport....not really.
I'll take a photo of the plug when I get a chance and post it, the tracking on the plug is quite evident.
I read a lot of posts about people have miss/surge problems, so I posted this in the event that it might help someone.