95 c280 cylinder miss, P0303, How to troubleshoot?

[WaBenzer]

Bought a 95 c280 3 months ago. 133,000 miles and ran smooth except on 1/2 to 2/3 throttle would stumble a little but was bearable. Two weeks ago I was taking an off-ramp and it started loping. Would barely make it up a hill. Feels like a plug wire fell off. I changed the old platinum plugs with NGK regular ones. It didn't help. They looked worn but even discoloration (see attachment) compared to one another. #3 does look a just little shinier than the others, but what do I know? I'm just a licensed aircraft mechanic so am more familiar with air cooled engines. The wires looked ok and so do the coils. I didn't scrutinize them though. Still idles very rough at 500 rpm. Runs rough at normal speed too.

Tried spraying MAS cleaner on the MAS plus the other sensor (is it the temp bulb?) closer to the throttle body. No help. Tried spraying same on as many vacuum lines as I could find and no change in idle was noted. There is no coolant loss or oil loss. There doesn't appear to be any fluid exchange.

One independent shop I know said cat converter because it smelled like firework smoke does. Honestly, that's the first I noticed it. Another independent MB shop I took my other MB's to said, if it's rich, that could cause the smell too. But they weren't eager to blame the converter right off. They said the computer should help narrow it down.

Soooo I bought a scanner which shows only one code: P0303 and the book reads Cylinder 3 Misfire Detected.

Q: Does the omission of other codes mean that the problem does *not* involve them? i.e. fuel, electrical, etc?

Q: Should I next: Swap one coil with another and see if there is a code change? Should I erase the old code first? If so, then it's the coil. Do the wires come off easily or do they tear apart?

Or: Remove the #3 plug wire and see if that does nothing, then it's the wire?

Thanks!