First thing to do is search the archives. There is a mountain of information on stalling problems. You'll need a good automotive multimeter to test the various fuel injection sensors and the MB CD to get the correct values for the sensors - a lot of it is in the archives.
Your problem sounds exactly the same as mine. Mine was solved by replacing the Air Flow Meter unit - specifically the potentiometer - it tends to wear out. I also found that the zero position of the throttle plate on the air flow meter was incorrectly set and this can lead to idle surging up and down.
Unfortunately there are a lot of things that can cause idle problems so you'll have to work through them systematically. I would suggest starting with the mechanical issues first such as looking for vacumn leaks etc.
Read through as much info as you can find on this site it's likely your problem has been encountered before.