So it looks like I dodged a bullet. Or Forded a bullet. (Thanks,
troupatour, for that bad pun!) The car is running fine, and the check engine light is now off.
Jenny's stepdad recommended that I disconnect the battery for a little bit to reset the onboard computer. Voila! Looks like a new PCV valve (and affiliated hoses) was exactly what ol' Frieda needed.
Now, what to do about the mess o' kitty litter and oil in the garage...