Idle speed drops after few minutes

The car will idle fine when started, but after thirty seconds to a minute will drop very low and may stall. Replaced plugs, they looked ok, first O2 sensor, and have removed and cleaned the IAC. It looked clean. If I start the car with the IAC unplugged, now the car will not idle, so that seems to me to indicate the IAC is working and getting some data from the ECM. I replaced the O2 sensor due to a code pertaining to O2 sensor circuit bank 1 sensor 2. Cannot remember the number. I have cleared the code and no more have shown up.
I have checked for vacuum leaks, but so far have not found anything. Really wondering if these is another sensor that is giving the ECM incorrect data?