If this car has an idle control valve like my 380sl, you should clean it, test it, verify the electrical connection (unplug it and see if the same if so connection or valve is bad) and may need to be replaced. My car also has a warmup regulator. Because your idle is so high at warmup it sounds like the valve . If the connector is bad you can make a ew one with those butt end connectors at the parts store, crimp one end and slide other end onto valve.