1999 Chrysler Cirrus rpm dropping @ stop in gear

I notice that when at a stop while in gear, my rpms will drop down to the first line (500?) and the oil light will come on. The engine acts like it wants to die but doesn't.

also, I've had a mechanic check it out and put it on the diagnostic scanner they have. No codes came back. Notice that this only happens once the car has warmed up to the max safe temp..