Interesting but not uncommon.
Let's go back to basics:
If the #1 cylinder is lean or misfires, it puts too much O2 into the exhaust, due to all the Oxygen isn't getting burned in that cylinder.
Now the exhaust has too much O2 in it, the O2 sensor "sees" it's has too much total O2 in the exhaust, it interprets that as the entire system is too lean. So it richens ALL the cylinders, till the O2 drops to about right. It richens ALL of them, not just the #1. Now #1 is right, but all the rest are rich.
Too rich makes that carbon you felt. It's incomplete burning, if you measured it, CO would be high.
The computer gets it's information from the O2 sensor, which is "pushing" the mixture toward rich, so the computer sets a code lean, even though the actual exhaust is rich.
I'd start by looking for a vacuum leak near the #1 cylinder, or even an exhaust leak ahead of the O2 sensor. Ie. Hoses, injector seal etc. Carefully spray a burnable Carb cleaner around suspected leak areas. Many carb cleaners are water based and won't burn. Dribble some on the floor and light it, if it burns it'll work. When you hit the leak, the burnable cleaner gets sucked in momentarily, you'll feel a slight RPM change. Propane works even better.
It could be something as simple as a plug wire - easy way is to swap it with a known good one - not one with another cylinder. New doesn't always mean good.
Let us know.
Sometimes ya gotta think backwards, a vacuum leak, or even an exhaust leak can make it run rich!