Check Engine Light, Smells and Engine Died (but restarted and drove) on 2003 Chevrolet Trailblazer

Parked my car in the drive way. Decided it was time to put it in the garage. Started it and it started running rough. Put it in reverse and it died. It restarted, I put it in neutral, rev'd it a bit to "clean it out". I've checked all the fluids, they're fine. It runs rough and engine power seems reduced. Has sort of a "spuddering" noise a bit. Any clues? Have to take it in and get it diagnosed. They said it could cost anywhere from $100-$500 ... Fabulous.