The imrc is designed to open the secondary intake ports at around 3200 rpm, allowing more air into the system for greater power at higher rpms. At lower rpms (everyday driving), the imrc is supposed to keep the secondaries closed for greater torque and economy. Have you ever floored it at low rpms and noticed that at 3200-3400rpms, your intake gets delightfully louder?
If the imrc is indeed keeping the secondaries open, you are losing low end performance and efficiency.
The imrc box is located under the plastic "2.5 liter duratec" cover on the front of the engine. Pull the plastic cover off and observe the imrc and the cable extending from it----------out to the bottom of the intake.
You should see that it is able to pull on a couple of levers, connected to a large spring, that open and close the secondaries. Have a friend rev the engine to 4000rpms while observing these levers. You should see some action. If not, make sure the levers are properly attached (the rod popped of one of the levers once on my contour).
Or perhaps the imrc has failed, which is not uncommon. You can usually pick one up on here on the forums for a decent price. It's a pretty easy inspection.