So here's the back-story:
I filled up my car at the local gas station. It had been raining non-stop for the past three days and nights. 10-15 minutes later as I'm stopped at a light, the car starts shuddering, almost stalls a few times. Rough idle all the way home.
I limp home, guessing water in the fuel. Next day I go to Advance Auto and buy some fuel additives which are supposed to help with the water problem. The guy there mentions that he's had a number of reports of similar issues from this particular gas station (it's now out of business, go figure). Additives make things better but not fully.
2 tanks of gas later now and the rough idle is much better but not gone. Car seems to have less power and sounds a little bit raspy on acceleration (not noticeable unless driving near a wall which can bounce the sound back). My guess is that one of the cylinders is not firing, maybe needs a new spark plug?
The more worrisome thing is that as the car has started running more smoothly I've also noticed a smell of gas after startup (may still be there when running but I don't notice it then) -- coming from the exhaust. This seems to be in-line with the missing cylinder theory but I'm running blind here as I don't have much experience on this topic.
The car's a 1997 C280. 130K on it. It's old but mechanically the thing has been a tank so far (Inline 6 I think) -- very sturdy and responsive. I'm hoping that this whole ordeal hasn't done permanent damage.
Any insights would be greatly appreciated.