Lately, in the teen temperatures up here in PA, my 84 500sel has been stalling after idling very low for a minute or so. The idle is extremely low (like around 500rpm) at startup after its been sitting for more than a couple hours and the engine sounds really weak at first. Then, it almost seems like the gas stops feeding the engine and the engine dies. If I try to restart it right after it dies, it'll turn over but will die immediately if I don't hold down the gas pedal. Once I let off, it'll die again. That is, unless I keep feeding it gas until the engine is warm. Once the engine is above 60C, it idles and runs fine.

What could the problem be? I just changed out the idle control unit and it didn't seem to really help. Could it be the idle control valve, or maybe the coolant temp sensor?