Help Temp & RPM's
 

I changed out my O2's as they were throwing codes PO300 & PO155. Now when I start the car my temp gauge will start to rise then it will drop, the rpm's will start to drop as the engine warms. But when the temp drops the rpm's pick up rpm's. This happens until the engines gets to operating temp, I changed the thermostat and the heat sending sensor and that did not help. Anyone ever run into this, & what did you do to fix? Could it be the idle air control valve?