Since you haven't gotten any replies, I assume that none of the traditional solutions would solve your problem, so I'll give it a stab...I am going back to experiences I've had with some non-MBs I've owned.
I don't really know, but is yours carbureted or fuel injected? If carbureted, it might be a bad accelerator diaphram...if FI, then maybe a bad injector.
You may even have a dirty fuel filter.
Have you checked your spark plug wires and your ignition coil(s)?
I had a Mazda that did just that, and it turned out to be a cracked air diaphram...are your intakes solid, i.e., no cracks, leaks etc.
I had a Z-24 with a bad air flow meter that would not maintain an idle until that was replaced.
Just a start...hope you pinpoint the problem soon!
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car