Engine missing when idling - 380sl
 

I've got a 84 380sl which is missing when idling once the engine is warmed up. It seems to be getting progressively worse this summer. Pulled the plugs and they are clean. I'm getting good gas mileage (22-23 mpg on the last two tanks). And when I'm driving the car appears to be running okay (can't feel it missing). It's only when I'm at stoplights that I feel the engine stumbling or missing. There are no problems getting underway once the light changes. Idling rpms are around 5-600 at idle and if I put it in neutral the symptoms diminish as the idling increases to about 650 rpm. The stumbling or missing does not appear to be happening when the engine is cold. Anybody have any ideas on what the issue might be?

Possibilies -

Vacuum leak - did the economy gauge reading at idle in gear change recently?
Injector seals
One or two weak or dirty injectors

My suggestions:

Check all vacuum fittings and connectors for leaks
Plug the cabin vacuum/AC line at the back of the engine and see if that makes a difference.
See if your booster holds vacuum - let the car sit for an hour, unscrew the the hose fitting, and see it you get a hiss from remaining vacuum
Pull the injectors out, have someone test/clean them, and put them back in with new seals.

No recent change to the vacumn guage was noticed. I'm leaning toward the ijector theory myself. At 140K they probaby need cleaning and replacing anyways.