High Idle

I have looked in the archives for help on this problem, but no luck. I have the high idle problem on my 1989 560 SEC and cant seem to get rid off it. With out spending a whole lot more money on parts I dont need is there a cure. I have replaced the idle valve, the idle speed control unit, the temp sensor and had the fuel adjuster on the intake adjusted with a co2 sensor in the exhaust pipe. I have been told it COULD, repeat COULD be my idle control valve on the bottom of the intake tube in the manifold. Should I go there or am I still fishing? BTW I did cross the two conections on the plug from the valve and the idle came down untill I shut the car off.
Also this seems to be a big job to replace such a small part. any help or thoughts would be great!
Thanks
Bill

Yes thats what I mean the throttle valve switch. When the car warms up, the idle increases. It tops out around 1100 rpms. When its cold it runs really well.
From what I have heard you have to remove the manifold to get to it.