Most likely your problem is the harness.....

That was the very first thing we looked at, including the harnesses from the ASR controller and the CCU. All were in great shape with nary a crack. Furthermore the main harness was out of the car and then replaced during a recent head gasket replacement.
I only WISH that it were so simple, but thanks for the tip.
Anziani

You will be surprised...

My bet is still the harness (but could also be the NSS)...

I am talking about the harness that attaches to the ETA...

And I would check the codes, they will point you in a direction, no dealer necessary...search and you will find all the information you will need.

http://www.peachparts.com/shopforum/tech-help/280952-connector-eta-rewire.html

JimF website:

http://www.k6jrf.com/MB_S500.html

The harness from the ETA was replaced by BBA when they rebuilt the ETA. No change at all. We've opened all harnesses at both ends. There isn't a single crack visible.
The NSS was replaced but I see that it still might be defective. I'll order out another one.
Arthur Dalton suggested starting the car with the Chained Tire Switch energized. Worked great for 5 days then went back to limp home. The fact that no warning lights show has to be the clue.
Error codes are always the same: Pin #8, code 8 Pin #14, code 14 However someone said that with the proper reader, sub codes would show. That is why I mentioned the dealer. My indie doesn't have an adequate reader.
Anziani
'93 300CE
'95 E420

These subcodes are for 1993 and up 2.8 & 3.2L M104 engines, but may apply to you.

Code 8 sub codes:
20 ISC system at lower control stop
21 ISC system at upper control stop
22 CC or EA indicates limp home mode

For the above I would check the throttle linkage, I remember this happening to me on my M119 engine: the plastic piece at the end of the throttle linkage broke, and the cable had too much slack, going into limp mode. I have been running with a configuration of cable ties for a while without any problems:o

For below I would check the switch on top of the accelerator pedal

Code 14 sub codes:
007 and 224 CTP switch (S29/3)

Thanks for your input. We checked the cable. It had the correct slop. There was nothing impeding it. In fact the control mechanism is quite straight forward on this car.

Took us a while but we finally found the micro switch on the throttle linkage. Figured "ah-hah that was it!" Replaced it with OEM. No change. Tomorrow we are installing a used CCU. I don't have a lot of hope that this will cure it but we'll try. My guess is there is some simple connection that is intermittent on start up only.
Anziani

Gents,

What’s the condition of your crankcase breather hose(s)?

I have not seen ASR/limp since mid-Spring time but expect to at the first instance of cool weather.

For a long time I have been sold on the battery (6+ years old) as root cause because, if the problem is electrical, it is the only component that reacts to swings in temperature/high humidity so consistently, and whose gradual deterioration would coincide with the narrowing range of temperature/humidity in which the fault occurs.

Unfortunately, that decline seems to have leveled in the past year. This summer, despite the high humidity, and no battery maintenance, I have not (yet) had a single ASR/Limp event, which is odd. If the battery is failing, I would think it would be in its death throes by now but it is still going strong.

After my emissions test yesterday, HC numbers were higher than 2 years ago, and much higher than 4 years ago. The car passed with room to spare, but I remember when it was blowing zeros.

If HC is high then the engine is obviously running rich. The O2 sensor is new, MAF is fine, so somewhere else is an air/vacuum issue causing the computer to overcompensate with added fuel. Supporting this is the code 6 – faulty idle speed control -- the DM would return after going into limp mode, which I understand is airflow related. Finally, although my idle is very smooth, I sometimes feel random, minuscule bumps and rumbles as if the fuel/air mix is fluctuating in a small way, as if a leak somewhere is causing it to not be constant.

Is it possible the culprit could be my oil-leaking (and thus air-leaking) crankcase vent hose – the one that runs from the intake to the back of the water pump/tensioner assembly? Shown here:
http://www.peachparts.com/shopforum/tech-help/296465-what-oil-hose.html

It is the only other visible component whose rate of deterioration would seem to coincide with the appearance, acceleration, and plateau of the ASR/Limp issue.

Is that hose designed to hold any measure of vacuum -- or, conversely, positive pressure? Could its leakiness create an implausible condition that throws the car into limp mode, particularly when the air is cold?

Eric,
I had a new head gasket installed and we replaced all hoses while the head was removed. I'm sorry to say I still have limp home about every other day. The temps here are now in the 105-115F range. Doesn't seem to make a difference with my car. Our guess is that it is a relay that does not fully pull in when the car is started. as soon as it cools down, I will get back on it.
Anziani
'93 300CE 200K
'95 E420 122K

Since you are not getting the ASR light on the bottom line of indicator lights, it does make sense that yours is not an air issue.

Even if it does not eventually resolve the cold weather limp problem, I at least hope the new breather hose I install this weekend will completely smooth out my idle.

Is there a list or chart of conditions that would trigger limp mode?

Eric,
I don't recall seeing a formal list but there are many things that will trigger it. Different size tires
Defective wheel speed sensors
Defective brake light circuitry
Defective hidden micro switch on throttle linkage
Defective brake light switch
Defective OVP
And of course the ETA/wiring harness.
I am sure there are more. Maybe someone else could add to this.
Anziani
'93 300CE 200K
'95 E420 122K

Installed new breather hose yesterday. Results inconclusive so far.

The car is Very quiet now (engine imperceptible over wind and tire noise with windows closed); idle is 98% smooth, especially after the engine reaches operating temps. However, I attribute all this to the new (Wahler) thermostat I installed the day before.

The car previously would run a bit cold, at about 81-84C when cruising on the highway, and about 95 -105 in stop and go with the A/C engaged. Now 85C is the new floor and it has not yet exceeded 100C. (I am guessing the computer was previously assuming the car was not warmed up and was pumping more fuel to help it do so, thus the noisier ride, similar to that on initial cold start.)

There is some mild vibration that I attribute to the solid rubber engine mounts I recently installed. I may swap them out for hydraulics to dampen the vibration.

Fingers crossed.

Last night the temps dropped to the low 60’s/upper 50’s, which historically guaranteed an ASR/Limp fault the next day. However, that did not happen this morning but it could just be a fluke. I’ll know for sure, after it gets perhaps 5 to 10 degrees colder overnight.

Otherwise, with cooler drier air (and more concentrated O2) the car is running beautifully. Not sure how much of that, if any, is related to the new breather hose.

Eric,
Keep us "posted" on the temp thing.
Anziani

So far, so good. Last night was also in the 50's and no issues today. Would be great if my problem was air related all along.

Cold and damp is the real gotcha. Perhaps a hurricane.