Several weeks have gone by, the car has been in the shop for several days, but the stalling continues.

My own mechanic replaced the plugs plug wires, distributor cap and rotor. No change in stalling behavior.
As weather warmed up, stalling became more frequent. Last 2 or 3 weeks, the car stalls nearly every time I drive it. Always starts OK, then stalls as I slow for a stop or turn in the first mile or two. Usually, I have to apply the gas pedal to get it to re-start. That is, I cannot start it the way you are supposed to, with your foot off the gas pedal.

My own mechanic referred me to an MB dealer that he claimed had a good technician team and would probably help. The MB dealer had the car for 3 days this past week. They measured the "lambda," whatever that is, and found it was "way out of spec," and adjusted it. And the mechanic found there was a pin on the connector between the voltage regulator and the alternator. They recommended replacing the voltage regulator, which I agreed to. They supposedly tested all sorts of other things, found nothing else wrong, and found no codes in the computer. It cost me $350 for their efforts. Plus the previous tune-up cost was about the same, as I recall.

The car started OK when I picked it up at the dealer, but the engine probably was not cold. Yesterday, we had snow and I left it running while I cleaned off the car, so it was so thoroughly warmed up, it might not have stalled anyway. It did not stall later in the day, in several trips at varying intervals. So I thought it was OK. I even imagined it was idling at a higher RPM and was idling smoother. Probably I was just seeing what I expected to see.

But today, when I started it first thing this morning, it stalled just as in the past! No improvement. It stalled 2 or 3 times in the first 2 or 3 miles of driving. Even stalled just as an ambulance was coming up behind me and I could not get out of the poor devil's way! Very upsetting.

This afternoon I spent a couple of hours reading the technical manual and trying to figure out the very complicated engine control systems on this machine. My interpretation is that there is a function that adjusts the idle speed during the warming-up period, when the coolant temp is below 80C. I note that the coolant temp sensor is the only signal that goes into both the idle control and into the control that delays the upshift from gear 2 to gear 3 when the engine is cold. As I noted above, I think, the car does not consistently operate in that delayed upshift mode. So I suspect the coolant temp sensor or the cable that feeds the signal to the control systems.
I tried to test the coolant temp sensor, but could not find instructions in the manual for how to do it. I could not see how the cable comes off. Does it pull straight up? Or does it unscrew? Or does it come off at all? I have a good digital ohmmeter, so I was going to measure the resistance and compare it to the specs in the manual.
There are many other devices and functions that could be wrong, from what I can see, and I do not know which of these the MB technician tested. SO I could be leaping to conclusions regarding the coolant temp sensor.

Since I have already spent about $700 trying to correct this problem, and since the mechanics obviously would have tried the obvious and common things first, I despair at the thought of paying these guys for more hours of witch-hunting. So does anyone have any input, suggestions, or further comments?
Thanks!

Hardly ANY modern cars stall like this. This is not only aggravating, it is downright embarrassing!

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DavidB29
1992 300E with ASR
35 years of Diesels until now!