I now have about 11K miles on my F150 2001 Ford Screw. I noticed rough idle. Its not all the time. Sometimes it idles pretty smooth. At other times its very noticable. I suspect the idle fuel metering system somehow is not consistent when it sets up the fuel air/mixture. Seems to idel better when its cold or after driving on the freeway.

Anyone have any ideas how to fix the problem? Ford dealership I took it to says nothing wrong that they can detect.

 

I had the same problem. Switching from regular to premium solved the problem. I'll try mid-grade after a while to see if the problem returns. It's expensive, but the upside is that I get >22mpg (Canadian) on the highway, and the truck is only rated for 20.