HELP??!!!

Since you don't have a performance tune, 87 octane is fine. Make sure you're not getting crappy quality gas, though.

Where was the plug drenched in oil? Near the electrode (the part that its INSIDE the engine?), or the top part of the plug that sticks out of the head (where your coil sits on top of the plug)?

Either way, it sounds like you're experiencing a misfire. If the part of the plug that sits inside the engine is covered in oil, you have a big problem. Either valve guide/seal or a damaged piston or piston ring.

If it's the top of the plug where it sticks out of the head, you could have a valve cover gasket leak and oil is fouling the connection between the spark plug and coil pack and causing it to misfire.

If you have access to a compression tester, I would perform a compression test on at least the cylinder with the oily plug. I would go ahead and do the rest of the cylinders and compare the results. Depending on your mileage, a healthy engine is going to be between 150-180psi per cylinder, and the cylinders should not vary more than 10% of each other.

The nose you're hearing... is it a ticking, tapping, knocking? Is it a light noise, or something deep and heavy? The noise on top of having oil potentially in that cylinder is pretty concerning.

Check the oil on your dipstick... wipe the dipstick onto a clean paper towel or rag. Are there any metallic shavings in the oil? What is the color of the oil? Does it smell excessively of gasoline (a little gas odor is going to be present)?

What led you to replace the O2 sensors?

Have you checked all your vacuum lines?

clean your IAC and see if that helps the bouncing idle issues...