93 300D jerking when wet
 

I have a 93 300D turbo 2.5. I have had a couple instances when the car seems to be jerking or pulsing/surging or whatever when the motor is accelerating or under load. It is combined with puff of black smoke out the tailpipe during these times. I guess that means it isn't burning all the fuel?? The car idles just fine and cruises OK but when I accelerate or go up a hill it lunges or delays (can't exactly tell if it is cutting out or kicking in). Feels kind of like the turbo kicking in if you will. Now I have noticed this only happens when it has been driven in significant rain. I leave it set for a few days and it is fine again (same fuel, just the car dry's out). This has never happened when it is dry conditions. Any ideas what's the deal? This is the vintage with the crappy wiring. Could I have something electrical? It feels like one of the baffles on the intake are pulsing but that may just be a bad guess but that is what I have in my mind. I don't know much about these things but the intake on mine has at least 1 baffle deal with a lever on it. Where do I start? Thanks!