Intake Gaskets! Intake Gaskets! Intake Gaskets!

They are likely leaking, letting air in that is unmetered. The O2 sensor code is probably a side affect.

It could also be the fuel pressure regulator isn't high enough, but this engine is notorious for Intake Gaskets leaking. If you reused the old ones for the S/C install, there is your likely culprit.

Nate