To follow up, I got a P0421 DTC immediately after completing the carbon cleanup. I had to crank the engine for a few minutes before it slowly came back to life. I'm guessing I left too much Berryman B-12 in the intake manifold, and perhaps some seeped into the combustion cylinder. I've since driven to 100 miles and changed the oil today.
B
efore I start changing the O2 sensors, I'll try the Scotty Kilmer laquer thinner trick. Dump 1 gallon LT per 10 gallons gas and drive at highway speeds for 150 miles or rev at 2500 RPM for 30 min.
Before my oil change, I also still have some occasional misfires, but a Ford Focus website said 1 misfire per 1000 RPMs is not bad. On the way back from buying LT from Home Depot, I had zero. Go figure.