I have this little problem with my car. It's happened twice, both under similar circumstances - after driving on the highway for around 1/2 an hour on a hot day, the secondaries stop opening. The first time it happened, everything was back to normal after I let the car sit for a couple of hours. As for the second time, it just happened this morning and I haven't driven the car since but I have a strong feeling everything will be fine when I drive it tomorrow. The fact that this problem seems heat-related makes me wonder if the ECU has programming to disable the IMRC based on readings from the IAT? Note that I have an SVT airbox and for now the IAT is just dangling in the engine bay (I've been too lazy to drill a hole for it in the airbox) and hence it should be reading higher temperatures than normal. Does this make sense? If not, any idea why my IMRC failure seems to be related to heat?
By the way, the Duratec with non-functioning IRMC reminds me a lot of the Zetec, especially with respect to the power curve above 5000 RPMs.