I agree with MBG Doc about running rich causing the rotten eggs smell. If it only happens intermittently, keep a log of the situations in which it is noticed, e.g. cold engine, cold day (40Deg F or less), what accessories are running, etc. If it really dies, perhaps idle stabilizer is not getting adjustment signal for added loads such as AC, or is getting signal and not working. Even if you can't find the problem yourself, keeping a situation specific log will help the professional technician know the best places to start looking. Just make certain you keep a copy of the log in case the first person doesn't fix it.