I replaced the spark plugs over the weekend, though I’m not sure that it was necessary to deal with the Check Engine Light problem. The light had gone out when I’d finished, but since I had to disconnect the battery before messing with the plugs, I’m willing to bet that the new plugs weren’t responsible for correcting the problem. Either way, the service manual recommends replacement at 60 months or 60,000 miles, so it was probably a good idea to do it, especially if I intend to sell it.
Today I went over to AAA to deal with my mileage problem. When I registered the car last year, the woman helping me keyed in 060702 for the mileage… but it was actually the date! Anyway, AAA was pretty helpful today when they did the title verification process. I should have a new title with the accurate mileage within a few weeks.