so i was driving down the freeway yesterday and i'd get a check engine light and the engine would just free rev, like it wasn't put in drive, or any gear for that matter. then it'd go back to normal. it did it a few times. was wondering what to expect damage wise and what might be the matter with it. also, there was a sulfur smell that we thought was coming from outside the car, turned out it was coming from the car! would this be from transmission or from a overcharging alternator?