'99 5.0 rough idle

[hitsmanj]

Searched and still not clear.

Left my mother-in-law sitting in my 172000 mile XLT yesterday for about 25 minutes with the engine running (insert own joke here, she was cold). Came back out and engine was idling rough, smooths out a little during acceleration, but still running rough, also strong smell of gunpowder. Thought it might have been bad gas as I had gone cheap on my last refill at Murphy's during a road trip 2 days previous and the tank was near empty. Full tank of good gas and a dose of STP for any potential water issues and it is barely smoother. Plugs and wires replaced about 20,000 miles ago. EGR replaced about 5000 miles ago from CEL issue.
Any ideas? Please don't get too tech, I'm not a mechanic, but know which end of the screwdriver to hold, what not to hit with a hammer, and many advanced uses for duct tape.

 

[nssj2]

sounds like a catalytic converter went. The sulfur (gunpowder) smell is usually associated with that, and a clogged cat screws with the idle. Look under it after some night driving with a heavy foot, and if its clogged, it'll have a nice red glow to it. You have 4, so its best to do some investigation before replacing them and hoping for the best.

Any CEL or white/black smoke out of the exhaust?

 

[hitsmanj]

Thanks, Jim, I'll give that a look

No smoke or CEL