Rough Idle, Blown out Vacuum plug

[jklnbrg]

I have a 94 XLT 2WD with 150,000 miles.
Recently the engine has been running very rough at idle and low speeds with idle rpm's hovering just above 500. Occasionaly the car dies particularly when shifting into reverse.
A backfire at low speed was followed by telltale hissing from the vaccum distribution. A plug was blown of. The plug has subsequently blown off 3 times now.
I smell an odor from the exhaust but no exhaust smoke even under heavy acceleration. (not a gasoline odor but closer to rotten eggs but not quite that rotten)
Engine performance seems smooth after gaining speed and mileage is around 18 mpg with the A/C.
Ideas? Hints?

Thanks!

 

[jimbo74]

rotten eggs sounds like a cat problem....

 

[jklnbrg]

The nearly rotten egg smell is less that than exhaust/gas smell.
I've never had the check engine light come on (except at start-up)