the 950 RPM is right on the money for a 'cold' engine. Probably the temperature switch has failed or has a bad connection. I have no helpful hints on why the computer is trying to lean out the engine--except when at idle, it is in the 'open loop' mode and the computer puts out a preprogrammed amount of fuel. The O2 sensor is not involved. If your is trying to use the O2 sensor at idle, the idle switch is not closing, telling the computer "I'm not at idle or wide open, so use the oxygen sensor output to adjust the fuel/air mixture to 14.7/1." Since at idle the O2 sensor is not hot enough to send out the proper signal, it can really screw things up.