If you have a 92 and have been "on it" the full throttle fuel enrichment may have some extra byproducts being burned off in the cat. This could be the culprit right there. Of course, tinkering with the coolant temp and/or intake air temp sensor could also do that... I've heard that high sulfur content fuels can also produce a "rotten egg" smell in the exhaust but I'll defer to Benzmac on the fine print.
Hope this helps...Lee