Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accurately.
the iac valve is located on the back of the throttle body housing. it is the size of a half can of redbull. try tapping on it with a small hammer when it is acting up. if it clears up, that is your problem.
Not sure about the IAC. Didn't see anything that looked like Red Bull. :-)
However, in my banging around on thingsI think I did finally find the problem - a large vac leak in the elbow of the large line running from way in back of the throttle body to the passenger side valve cover. Is that the EGR valve or the PCV valve or neither?
Soon as I put my finger over the gaping hole, it idles right down nice and smooth. Looks like it wasn't the IAC, but I do appreciate the help. I'm sure I'll be in touch again.