I think that the cycling at start and stop is normal and that is the system checking itself and that is why there are no diagnostic codes. My theory is that the system does not check IMRC (correct spelling, thanks) during vehicle operation, just at start and stop. The cycling is perfect every time, seems like it is programed to do so. Which I had another car to observe this one. I will be on the lookout for one. Maybe test drive one on a used car lot today to verify.
It really can't be a vacuum issue because when I supply an external ground directly to the vacuum solenoid the flaps close instantly and stay that way al long as the external ground is applied. It seems to me that the fault is in whatever path that ground signal to the vacuum solenoid takes to get from the ECU to the solenoid. From the wiring schematics I can find online it seems like the EGR valve is in the mix somehow along with the cylinder head temp sensor and of course some engine rpm signal. The EGR valve is cheap ($20) so I was thinking of replacing that.
I know that I should probably just leave it be and drive it but I am very curious what is causing this and the extra 10% in fuel economy would save me $200/year.
Many thanks for all of your comments and time. I'll keep poking around a bit. I am surprised that I have been unable to find a detailed description of the control logic in the online service manual?? Maybe Ford considers this info proprietary??
Anyhow again thanks, Mike