try changing the IAC motor, if they go out of adjustment or get clogged the computer constantly opens & closes it trying to reach the specified idle, unable to do so..I replaced the O2 sensor a few months back, and the profile just doesn't seem to match the IAC. I mean it's obviously not stuck; there wouldn't be any mode of failure that I can think of that would make it have a mind of its own other than a intermittent connection, but all the connections appear to be ok.
I did find one problem though - in my infinite wisdumb I must have timed it with the coolant sensor connected. When I checked time it was fine when connected but then it jumped down to 4 degrees when I disconnected it! I'll take it out for a drive today to see how it did.
your coolant temp sensor when unplugged makes the computer go into timing adjust mode and attempts lowers the idle to 700rpm so this is normal.
another cause could be your throttle position sensor, or a vacuum leak