Usually the rotten egg smell is an indication of a plugged up catalytic converter, might have been caused by using cheap gas?

I once owned Honda Civic, it would smell like eggs even at idle, then one day I couldn't pass smog. So I took the catalytic converter out and cut the container open, which housed the catalyst. Upon inspection it was plugged up with a grayish glazed material, amazing if could actually run like this. So I installed a new one and all smell went away.

So you might just want to put it on the rollers for a smog test and see if it can pass.