That it only happens when warm makes me think there may be a bad upstream O2 sensor involved since the computer only refers to them once the engine has started to warm up. The downstream O2 sensor on the catalytic converter would not cause problems like that so if you replace the upstream, don't waste your $$$ for the downstream sensor too. Go strictly for an NTK O2 sensor, no other brands... especially don't use a Bosch O2 sensor. A bad upstream O2 sensor can cause several problems like a bad idle, poor power, reduced mpg, etc. They go bad like spark plugs do so they do need to be replaced occasionally. Again, I would not bother replacing the O2 sensor on the catalytic converter, it only monitors the cat... it won't affect how the engine runs like the upstream O2 sensor does.
Though you cleaned the IAC sensor, a dirty IAC commonly causes this problem, it sounds like you did not also clean its orifice in the throttle body the IAC fits into. If the orifice (hole) the IAC fits into is dirty it can also cause this problem. There's an easy way to clean it which also cleans the IAC... with the engine running at IDLE rpms, don't rev it above idle, spray 1/3 of a can of throttle body cleaner into the TB. The engine will stall and die, that's ok. Restart the engine and do it again. Remember to keep the engine strictly at idle rpms while doing this. Raising the rpms up off idle rpms will cause the throttle body you spray into the throttle body to bypass the IAC and its orifice. Keep spraying the cleaner into the throttle body at idle rpms until you've gotten 1/3 or so of the can through the IAC and its orifice.
