very high idle problem. Please come in
 

I just did my head gasket and the car was running fine in 3 days. Day forth it developed a new problem. After start the car, it rev all the way up pass 2k RPM and stay up there. I step on the gas to rev it higher then left the pedal, the RPM stayed up there and doesn't come down.
After 1/2 a day I notice the problem a little more detail. When I shift it in gear (either R, D, 3, or 2) then the RPM come down to normal position doesn't matter if I step on the gas pedal to drive, leave the car running without steping on gas pedal, or step on the brake.
If I shift the gear to either P or N, then RPM came back up real high again.
I affraid this is the tranny problem but someone suggest it is the idle control that go bad. So I went ahead did some search on the net about idle control valve and found that the problem of the ICV makes the car hesitate/surge at idle. After the car is running pass some RPM then it's ok. As you guys can see my problem is a little bit diff. I don't want to shread out almost $200 bucks for a wrong part so can someone shread me some light? Anyone know where is the ICV located in my car (1990 300se) and how does it look like? Any picture somewhere I can view? Also how to test it?
Thanks in advance

The big rubber hose going to the intake from the ICV?

I would go the same way as brewtoo, check all the hoses connected to the ICV, and clean the ICV.
Do a search on ICV (and it hoses), tons and tons of information with pictures in many cases.