Idle jets!

I pulled each one out and blasted some carb cleaner through each one. Several were visibly clogged. The car is in much better spirits now! It still has that shake, but it's around 2,000-2,200 and less pronounced, and there is a great deal less flatulance all-around.

I wonder if it had anything to do with effectively running with no air filter for who knows how long...Thanks, y'all!