Well, the first thing I would say is don't confuse me with a real mechanic. There's plenty of them on this forum and I'm not one of them. Most of what I know in this area is from being subscribed to 3 mailing lists and reading this forum in an attempt to solve the problems of my own vehicles.
Unfortunately, instead of having an answer, I have more questions. First, what have you replaced recently? Second, does it start fine the first time of the day that it's started? How about after it's been sitting for just a few minutes after getting warm?
From your previous thread you mention that your ABS light comes on regularly, even though you replaced the OVP. Are there any other odd things happening?
Let me try to restate what I think you're saying. After you've started the car and the engine temperature is cold, it idles and runs fine, until it gets to about ? on the temperature gauge and then it idles rough and hesitates on acceration for a few minutes. You have to rev it to keep it from dying at idle. As soon as it reaches operating temperature (~87C), it idles and runs fine again.
I know that's annoying, my brother is a reporter and he does that to me all of the time. But it does help clarify things for me.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino