Very good qusetions and I thought about that ater my reply. I don't know. I guess that it makes no sense the Idle valve would suddenly open and than stick open after being in the proper position.

You cannot ignor the fact that your high idle is caused by the idle valve being open otherwise unpluging and repluging would not affect idle.

The ICV is controlled by a circuit board called the idle speed control unit located under the carpet on the passenger side.
Anything is posible with a mercedes electronic circuit board!