idle, stalling, and bad smells...
just trying to find out what's wrong with my 95 325i and I came across your post. My problems started a couple of months ago exactly like yours. Started car, rough idle out of no where, bad smell, and then pressed gas and killed it completely. I did see and read the engine code though, it said there was a problem with the O2 sensor, located on the exhaust directly in front of the catalytic convertor. Now this will sound odd, but I read somewhere at the time to disconnect your battery cable for a few minutes. I did this and it actually fixed the problem immediately for quite a while, it happened again weeks later, and I did it again, fixed it again. I did actually replace the O2 sensor since then, though it's hard to tell if it has had an effect.
Recently, the engine is very unhappy it idles unsteady and stalls alot, going to check plugs tomorrow. It runs fine at highway speeds, just go tback from thousand mile trip, just troubled at stoplights. I also have noticed the these problems have happened when I've been running on fumes, and just after filling up the tank. In fact yesterday, the car wouldn't start at all right after I filled up the tank from near dead empty. Took five minutes of trying before it started.
I'd appreciate any insight from anyone as well, thanks.