that is usually the IMRC but can be a vacuum line or wiring also fuse a blown fuse 12 that is on the same circuit as the upstream O2 here is a PDF of the IMRC ,does it set the code at idle or just at high rpm also helps diagnose it ,if it sets at idle it could be stuck open,also the vacuum solenoid should have power at all times and the PCM grounds the other pin at high RPM so try grounding it to check the vacuum solenoid operation
