Intake Manifold Runner Control. Our heads have a primary and a secondary intake port. When the car is under 3250 rpms your running off of one port. Once you past 3250 the IMRC's open and then run off of both ports. This design was created when the 4.6's came out to give them a little torque down low. You can feel it "kick in" around 3600rpms. With 112k on the car I would try to clean them first. If your plugs and wires are good then try the cleaning the IMRC's. Just do a process of elimination. But as Ryan said get rid of that MSD. But as your description it does sound like they need cleaning. Hope this helps. -Mark