Our 2000 t&c 3.3 w/120,000 miles ran fine until the other day when driving it started to run rough. Then, when accelerating, it would hesitate and I heard slight backfireing. Got it home and turned it off, smelled strong odor, like rotten eggs, and loud pinging. Could the cat be toast? My mechanic is out of town and I don't trust anyone elese to look at it. Any ideas? Thanks.