On the drivers side inner fender wall, down above the AC receiver drier, there is an ignition control unit. It has a vacuum line going to it. MAke sure that line is still there. It will be near the ABS motor. Worth a shot, since we are covering every avenue. I know it will idle weird with that hose detached.
As for the cold start valve, hmm, honestly not sure, but If it still does it when warm, maybe not. Another thing I was thinking of, since you said the engine flucuates...is a bad intake gasket.
Since you said the idle gets better when warm, maybe the engine expands, and thus sealing most of the leak, which would explain why it idles rough when cold. Although I never seen one go bad on these cars before. Oh well, worth a shot. Try spraying some carb cleaner around the intake when its cold and idling funky. If the idle jumps, you have a leak.
Keep me informed,
93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K