Rough running plus sulfur smell from 1999 V70
 

My 1999 V70 non-turbo recently began running rough. I brought it down to the auto parts store and had them read the codes. Came back the #5 cylinder was mis-firing.

I replaced that coil, no improvement. Then replaced all 5 sparkplugs; no better.
I also noticed a sulfur odor coming from the exhaust.

Any ideas?