The IRMC (intake manifold runner control) is the device the controls opening the secondary butterflys in the intake manifold. Those butterflys are shut until the engine gets about 4000 RPM part throttle or 3400 RPM wide open throttle. It provides better low rpm throttle response and improved fuel economy whil allow for better performance during higher engine speeds.
The IMRC control box is mounted on top of the front valve cover, under the trim cover. It has a cable that attaches to the linkage on the lower intake manifold below the throttle body.
One of the common fauilures is that the cable frays and sticks and binds inside the housing. Sometimes the electrical motor inside the box fails or the electronics get flakey. The only real cure for any of this is to replace the IMRC control box since there is no practical way to repair any of these things. The box is a bit pricy so shop around.
There is a plastic clip that attaches the secondary linkage from one bank of the lower intake maniflod to the other that sometimes breaks so make sure it is OK before replacing the box.
A contributing factor to the box failing can be from sludge forming on the secondaries inside the manifold. It would be wise to clean this along with any other repair that you do. There is information on cleaning both from disassembly of the manifolds and from running cleaner into the manifold while the engine is running. I do the cleaning without disassembly and it works well for me but others say that the manifold teardown is the preferred way to go. Do a search and you should be able to learn more about both methods. The teardown method is in the FAQ section.
Good luck and let us know what you find.
