Sounds like a catalitic converter going bad, or already gone. You can try putting a bottle of techron adn do an "italian tune-up", go to the highway and let it go for a while. It that does not clear the idle and the smell...disconnect the catalitic converter and see if that makes it better. If it does you need a new cat. $
On the other hand, a bad EHA normally leaks...
I am sure you will get more suggestions but, at least it is a starting point.
Good luck!
