Always check for vacuum leaks with a stall situation, especially when heavy on the brakes.
Second...and less common, is a stall situation when cruising along straight line, no turns, even gas input, just maintaining speed....and she quits. I have seen bad spark plug wires arch enough to shut down the motor, roll back the key, turn to ON position and comes alive again. It took me a year on my sisters audi 4000 to figure this out. Dealer could not find, indy mech could not find. Could never reproduce in a shop. FYI..wires were only 1 year old, and broke down real quick for some reason.
Moral is.... every once in a while, open your hood at night...pitch black, and see if you are getting a light show.

The mixture tweak seems to have helped, though its too early to know if its 100% cured. I'm curious about the duty cycle discrepancy. But since the car runs fine, I'm not feeling compelled to locate and swap out ECUs, etc. Plus I'm a little afraid of what I might find, and/or breaking something else in the process.

The ratio at 2500 rpm hovers around 70%. Idle is now 70-76.

I'd like to find out if any other 1985 380s (86560SEL?) want to be at 70% duty cycle instead of <50%. Or do I own a total odd-ball?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

as i originally said the two i worked on last week at work were set around 35-40% when i checked ignition timing one was at tdc and the other was at 11 before. both ran fine so i left them as is. timing can also affect the ratio %. you may check and see what it is at, should be with vacuum disconnected and plugged

I had the identical stalling problem with my '88 260e. The culprit turned out to be the airflow sensor pot. It is a variable resistor on the front of the airflow sensor that senses throttle positon. The carbon on the circuit board wears out first in the idle range (where it rubs most of the time). A slight blip (loss of signal) is enough to kill the engine with no warning at all.

You may be told that the entire airflow sensor needs to be replaced but I bought the sensor pot at Olyparts.com and changed it myself. Hasn't stalled since.

I don't know about the timing yet, but I do know I have it slightly advanced to use midgrade fuel instead of regular. The power seems a little better that way.

About the duty cycle, heres what happens:

The car runs best at around 70-73%. If I turn the mixture adjustment to the right (rich) the reading goes up. It eventually maxes out at 90%, which I assume is the limit where lambda stops working. If I turn it left (lean) again and go towards 60%, it really starts chugging and sputtering. So what does this mean?

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

did you say if you had looked for vacuum leaks?

I inspected, and replaced anything that was cracked or leaking. Including the tube that goes to the transmission.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

With the mixture adjustment, although better, the engine would still almost stall sometimes. I decided to pull the ICV and clean it out per the advice found elsewhere in this forum. A lot of black gunk came out so I wouldn't doubt things were getting sticky inside. Reinstalled, and its way better now.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

Just a follow-up. Cleaning the ICV has *completely* solved my stalling problem. I'm not positive, but it looks like it meters crankcase gasses into the intake, and not fresh air. That would explain the buildup of gunk inside. I would make ICV cleaning part of regular maintenance.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

To update, my 85' 380SE is still stalling when hot/warm, but it has not gotten worse, but it is getting old.

I phoned one of the local Mercedes repair shops and he said it could be the idle control valve, or the computer, or a vacuum line leak. Upon recommendation, I disconnected the idle control valve with the engine running and the idle did go up to 2000 like he said it should. Does this mean that the idle control valve is OK? Seems like the stalling is worse when going into reverse and it harshly engages into reverse, especially when the engine is hot. I am assuming this harshness is a different problem.... ??

He said to use brake cleaner and spray around to check for vacuum line leaks? This seems dangerous, since this is extremely flammable? Or am I being to paranoid? He also said I could remove the valve and spray WD-40 in it, but I am assuming this is if there was no change on the idle when I removed the connection from the valve? There was the RPM increase.

I do not know what else to do. I had about decided to get a brand new car, but after looking at them, seeing the prices and the low quality that seems to plague many of the cars these days, I think I may be better off keeping my 85' 380 for awhile longer (at least until the timing chain/rails break- then part it out, because with lifter chatter on the passenger side and 270K miles, I do not want to spend alot of money on it, as I have already got my monies worth out of it).

Any further advice about my stalling problem would be appreciated.