What is the warm-up RPM? wondering if the warm up idle speed is masking the problem. kinda sounds like a fuel leak and a vacuum leak. Kinda like the idea of replacing the O2 sensor. Still, the fuel smell sounds like a small leak under the hood. Let it run for awhile in the driveway and see if there are any drips or you can spot any leaks. (fire hose at the ready!). Take a real good look at the vacuum lines/fittings and injector seals.