on and off,how can I fix it myself?can I disconnect something or the choke itself and set the idling manually?

Idle problems with W126's are common, I have a 380SEC which idles too fast when half warm but is OK when cold and when hot.

There are multiple possible causes and while it could be the auto choke, look at the idle control module, the mass flow sensor (make sure it's clean) and make sure electrical connections are sound. Another trick advised by some is to set the spark plugs to a slightly wider gap. I don't think you can set the idle manually unless you get into the module, but I could be wrong. I would not consider disconnecting the choke as it is likely to mess other things up.

There is a lot of good information on various Mercedes Benz forums on the net. Search under "W126". Some of the archives in these sites will tell you almost exactly how to fix this yourself. It may take a bit of searching. I'd suggest the MB coupes site. Register and ask a question or check the archives for mention of idle. There are a people there who know these cars inside out. Some of them don't take kindly to foolish questions so think before you type (I'm not suggesting your question is foolish, BTW)

There is also a fair bit of stuff on the net about the Bosch K-Jetronic injection system which is almost certainly the one on any 380. Take a good look after searching "K-Jetronic".

when starting a cool to engine of a mercedes it is normal for fast idle, plus sluggish transmission until warmed..
after starting give it a few mins then rev it up a few times not to exceed 200000 rmps normal idle should be between 9-1100000 rpsdoing this a few times should cut the cold switch out and lower rpm's

You have fuel injection there for no choke! No idle adjustment! There is a idle vale on the left side of the engine down by what you think is the carb. replace it. Look on eBay for a used one and save a bundle. It is easy. there is an electric connection and a vacuum line hooked up to it. It is held in place with a 10 mm bolt. Do not mess with the engine as you will only mess things up and then you will be walking.