Same problem with my car too.
I have been scanning all the posts related to stalling for more than a year. I would like to know too. Last night I took the car to another old and very experienced mechanic.
He told me to put a can of injector cleaner into half tank of fuel and run the car for a few days if it still stalls he said I will have to replace the ignition control unit. The car did not stall today. I am hoping it gets cured.

I asked the Bosch service centre here whether they can run some diagnostics on this car and be able to tell me what the problem is. I got the answer that this car being an old one it does not have any electronics capability that can be diagnosed . The only thing they can do is guesswork and keep on changing parts till the problem is fixed.I further asked him whether the dealer has some instruments that will be able to diagnose the problem, I got the answer that they will hand me a list of all the parts needed for the engine to run which will be more than the cost of the car.
I have spent a lot of money on keeping the car looking beautiful and now I dont want to let it go.

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300CE 1989 Euro Model.
ML350 2011.