Another Smell

I have a 2000 Toyota Yaris, about 32000 miles and it had a consistent burning smell. My car is no longer consistently producing a burning smell, that is now occassional, but I do smell something else that concerns me a gas(but not gasoline) smell, slightly chemical. I let a mechanic check it out for me and he said it was the converter and nothing was leaking , but it does not smell like rotten eggs, just gassy(not gasoline). Could it still be the converter or something else?

I have experienced a similar burning smell as recent as last week from my 2003 Echo with 58k miles. This happens very rarely. It usually lasted for few days and then vanished. It is like the burning of chemicals such as electrical wires, oil or ATF, definitely not gasoline. I change oil and ATF, and do other maintenance on the Echo myself. It is possible that I might drip some oil or ATF on the engine block by accident. When the engine is running hot, the oil /ATF residues were burned and produced burning smell. If you had a mechanic work on your car lately, it is possible that this might also happen to you.