E320 Stalling, rough idle and limp mode
 

My 86 E320 exhibited stalling on start up which seemed to go away as long as I gave it enough accelerator to keep the rpm's up and it also ran fine around town unless I was stopped. However, on the freeway it went into limp mode a couple of times - which is very definitely not a safe thing to have happen.

After a thorough search of the forum, I found numerous possible causes but the culprit was the VOLTAGE REGULATOR. Easy to check, just put a meter on the battery with the engine running. You should have less than 15 volts. Mine was putting over 18 volts at idle which was causing havoc with the sensitive electronics.

It is located on the alternator and not expensive to replace.

Wow.... problem, diagnosis and solution all in one quick post.
Thanks