A couple of thoughts.

1. I chased a similar problem on my 560. My advisor, Peter Fuchs of Silver Star Motors, advised being sure the plugs and wires were good. His theory is that everything needs to be perfect during warm-up, but a marginal part will still function at operating temp. I blew this off and checked everything you have. Finally, the miss got worse and I was able to isolate it as - guess what - a plug wire.

2. That fixed about 90% of the problem, but I still had an occasional rough idle on warm-up. The remainder turned out to be a very small crack in the rubber connector for the cabin vacuum line on the back of the intake manifold.

3. Have you run a check of the on/off ratio. Maybe you are really lean so it runs crappy until it gets into closed loop and the lambda system starts to enrich.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe