FWIW: Most of these things are easily searched.
The IMRC (Intake manifold runner control) controls the secondary butterfly valves within your lower intake manifold (LIM)
When driving, and reacing an rpm of 3700 (3200@WOT) the secondary plates are rotated open to allow an increase in LIM volume, creating a surge in horsepower (you can feel that "kick" when you accelerate at those rpms.
The IMRC is the unit responsible for actuating those linkages via a cable (like a bike brake cable). Heatsoak usually kills the transistor within the silver IMRC box (located underneath the plastic cover that says "duratec" on it). Your problem is likely a failed imrc (dead due to heat), or a broken cable between that silver box, and the LIM itself.
Intake manifold cleaning can be done one of two ways:
the "on the car method" is a great method to "maintain" the cleanliness, but performed on a never-before-cleaned intake, it wouldn't do much good.
the other method is the complete rebuild, which involves pulling the UIM (upper) and LIM (lower) from the engine. It is NOT that hard, and both ways (whichever you should decide) are well documented under theduratec maintenance forum, in the duratec maintenance faq.
Ray
