OK...I think I have read just about every thread on rough idles and ideas on how to fix. However, I have noticed that the rough idle after engine gets warm on an M103, while engaged in Drive, and with break pedal on threads, have not had resolutions to the threads I have investigated (they just end and no post backs saying "Volia!"). There have been all sorts of "have you tried this?" and "have you checked that?", or "I would recommend looking at..." but ultimately the threads end with no closure. As everyone else has, I've replaced numerous parts and components on my 1991 300E but still have the same warm idle issue...when cold, no problem in Park or Gear at a stop (700+ RPM and smooth). When 80 c or higher, RPM drops to approx 500-550 and car shutters and struggles a bit with or without AC on...no diff.
So, has anyone out there actually resolved this issue in their old engine that can be shared? Seems there has to be a common solution as many. many Mercedes have had the same symptom.
Here is what I've done:
1. Replaced O2 Sensor (mileage improved)
2. Replaced Plugs (power improved)
3. Replaced Voltage Regulator (intermittent radio function and speaker output fixed)
4. Replaced Rotor (car starts much faster and stronger when cold)
5. Replaced OVP (No change in anything but needed to for confidence)
6. Cleaned out all Throttle components, ICV, linkages tight.
7. Performed Carb Cleaner spray test on all vacuum lines to no avail.
8. Replaced Fan and Clutch (clutch was frozen) but just works more efficiently now.
9. Adjusted Lambda Air Flow to no avail either way with load on engine and drive engaged.
10. Replaced brakes and car now stops on a dime.

Thanks!