Long story short I've found that the exhaust emits faint rotten egg smell only with a/c on (car in park, idling after hard run in hot weather). Turning a/c off clears the smell
The LTFT is -1.6 at this time. No misfire.
Will do some research if time permits.
PS I had dead cat on 87 Camry but never had any smell like this

 

I wonder if the A/C really doesn't have anything to do with the smell, it's just that the engine is working harder with A/C on, especially when the car is not moving after a long run. I'm thinking this is an exhaust or cat issue.

First guess - the catalytic converter needs to be replaced. Hydrogen sulfide is present in small amounts in gasoline, and is supposed to be removed by the cat. Bad cat = bad smell.

Second guess - exhaust leak before the cat. That would explain why the cat isn't cleaning it up, it never has a chance to get there. Cracked exhaust manifold, maybe?

 

I measured the cat temperature and it is within range 477 C at idle after 30 minutes drive
The smell happens only sometimes typically when idling after long hard run.
Thankfully, my next car project I am working at is CA smog exempt (1978 diesel rabbit )

 

You need therapy, DrJ. LOL

I've noticed that summer gas can occasionally emit more sulfur. This tendency is not as bad in the past 10 years, the sulfur rotten-egg smell used to be QUITE pronounced.

 

it comes and goes; (I measured cat temperature after 14 miles driving with a/c on and it reads about 525 degrees C which is same I used to see when the car was new).
Funny enough, the ECT (engine temperature) read 81 C and it was quite warm outside (84 F); perhaps this is due to fans running with a/c