One bank if engine not getting fuel not possible if fuel rail connected because it is a loop system unless blockage in the rail. Have you checked the pressure regulator and the damper units? Maybe some strange fault that is causing fuel restriction. What is your fuel pressure?
With one bank not receiving fuel the engine would run so bad I doubt it would idle any where near normal. Maybe some fuel getting to the one bank but not enough to notice on the plugs?
I assume you checked all plugs for spark and ohmed the coils?