From the description, it sounds like they are reading an IMRC (intake manifold runner control) fault, but it's hard to say without the actual code. The intake runners basically open up a secondary set of air intake ports above certain engine RPMs (3400-3900) They could be sticking because of carbon or gunk buildup on the lower intake or because on an electrical/mechanical failure of the IMRC actuators and linkage. Carbon or gunk buildup requires cleaning the lower intake manifold. (Which should mean UIM and LIM removal) Not sure on costs and work for replacing the IMRC motor/solenoid as I have the older vaccuum operated IMRC. (Try a search for IMRC in the problems forum.)
