first, make sure your air filter is in good condition, or replace it, it's cheap. Then tank up with premium unleaded and get out on the superhighway or other open road where you can drive at sustained high speed to heat up the platinum catalyst and burn out the gunk.
many cars make that stink when started from cold, because the converter can't convert all of the rich mixture that keeps a cold engine running smoothly. It's less noticeable with fuel-injected engines, because of the more-accurate fuel metering. there's sulfur in fuel additives; your engine isn't burning it completely and your catalytic converter is storing it and then releasing it as hydrogen sulfide when you add load to the engine and force more air through.try switching gas stations, or fuel grades; then try a thorough tune-up: replace the spark plugs, plug wires, fuel and air filters, and oxygen sensor, and clean the fuel injectors. If that doesn't do it, replace your converter.if the bad smell you smell is like rotton eggs or sulfur, it has something to do with the cats, a catalytic converter will get over heated if the engine is running too rich. Check the fuel pressure. Also, check the fuel injectors to see if they are leaking and scan the computer for fault codes. Your problem sounds like too much fuel is being put into the engine from the fuel injectors. Have the fuel injectors replaced. also, A/C will make this happen because the computer is enriching the mixture to account for the horsepower requirements of the A/C compressor.
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