The issue is more likely a problem with the idle motor. I wrote of my experience with this before, but it was similar to yours. Without the air conditioning on, the car did not always stall when you slowed down and put the clutch in, but it did it with pretty irritating regularity. Then, if you had the a/c on, it did it all the time. I also noted the a/c idle speed increasing feature worked erratically.
I had the Oxygen sensor and the idle motor changed. The idle motor is the aluminum cylinder between and under the intake runners for the number 2 and 3 cylinders. It is part of a system only a German engineer steeped in the tradition of "why make it simple when it is easy to make it complicated?" could design. Anyway this thing apparently spins a cylinder inside that has an orifice that passes air used for idling only when certain ports line up, or something. I am not clear on how it works, just that when it doesn't, you lose control of the idle function. Any abrupt or difficult idling situations and the car stalls.
Others on this site have reported removing the idle motor, filling it with carb cleaning fluid, and turning the mechanism by hand (through the port) and rinsing it out. Another gas rinse and then the inner rotating cylinder gets freed up and it goes back in, apparently ready for another lifetime of idle control.
I only mentioned the Oxygen sensor because it was replaced at the same time. It was not cited by the mechanics as the culprit in the idle fix.
Hope this helps, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)