'99 2.3L Kompressor
I wonder if the mechanic disconnected/broke/knocked loose one of the O2 sensors, especially the second one on the exhaust system. If the odd smell is more like rotten eggs, then you have a problem with your catalytic converter. Either it is going bad or one of the engine sensors (MAF, O2, etc) is so out of whack that it is throwing the mixture off to the point the cat converter can't keep up (and will soon be ruined $$$). What codes is your car sending out? Go borrow a scanner for free from the auto parts store and find out.