Josh,

I'm not an expert, but I've read a few posts from them regarding this problem, and it seems that when moisture plays a part in the car stalling, the problem is most likely electrical in nature, as opposed to a fuel delivery or vacuum leak type of problem.

I had a similar issue with my '87 300e. It would generally start up rather quickly, but had a bit of a stumbly idle, and just after warming up, was prone to stalling at low speeds. It would choke a few times, and die. This problem was more pronounced after a long rain, but mine would usually start later that day when it had dried up a bit, never did I have to wait a couple days! A couple times I darn near wore out the starter to get it to start, and babied it out of town (light gas pedal pushin' until it got up to speed). Once I got it on the highway, it was fine.

Anyway, I took it to an independent Benz mechanic who replaced a laundry list of things to fix this, distributor cap, rotor, ignition coil, new spark plugs and spark plug wires, OVP relay, O2 sensor, wiper blade, and after he was done, I still have a bit of a stumbly idle, but it hasn't stalled, and that was a couple weeks ago. I think it was the wiper blade...

Do you live in a perpetually damp part of the globe? Pacific Northwest, perhaps? When trying to start does it catch and then die, or does it just not catch at all when it's wet? If it does ever catch and die, how does it die? Does it go out fighting with a few chugs and some engine rocking, or does it just cut out, like someone flipped switch? You mentioned the distributor cap & rotor were changed, so I might think the coil maybe needed to be changed, too.

Good Luck,
Oak