If it smells like sulfur, it's vulcanite. Sulfur is added to rubber to harden it. If you can smell it, there's a good bit of oxidation that has resulted in sulphur being brought to the surface. And even if the cold water helped, I will bet you can taste the bitterness of the sulphur if you put the pipe in your mouth. You need to use abrasive to remove that outer layer of oxidized rubber in order to get to fresh, black material. All sorts of abrasives will work, some faster than others. George's method is the best, but not everyone has a buffer.
There are myriad threads on this topic which discuss many methods, most of which I've tried. One that works pretty well is using a Mr. Clean Magic Eraser, followed by some form of polish. The magic eraser will leave the stem looking rather dull, so it will take a fair bit of patience to get it looking shiny with just polish. Many like using a series of increasingly fine Micromesh brand sanding pads. Lots of ways to skin a cat.