My VTC was changed last August due to the classic start up rattle. I have since put about 3K miles on it and my over the winter mileage dropped to 23.4 MPG from 3 previous winter mileages in the 26 MPG range. The car currently has 29K on it. I talked to the service manager about this recently and he said without any codes or eng light indication he can't believe the VTC change is at fault. My question is, can the VTC malfunction in a way to harm mileage without throwing a code or eng light? I know the VTEC system is operational as I can hear it kick in about 6000 rpm but I'm wondering if the VTC is modulating cam timing changes as it should. I have changed oil and filter between the 5-6K mark since new and air cleaner is clean. Engine runs great, just mileage has dropped off too much I think.