Thanks, Darrin. The weird thing is I did put some miles on the car right after the new ECM and tune went in last year, no CEL. The car was then in storage for the winter (I did move it once, at a friend's house, from one garage spot to another, but otherwise it just sat with Stabil in the tank and a battery tender). Took it out a couple of weeks ago, and got the CEL shortly thereafter, in normal driving conditions. Cleared the code, it came back in 40 miles. Ran the tank down (thinking bad gas), refilled, cleared code, 40 miles later, it was back again. I would think most of the more serious potential causes would result in some noticeable running issues, and there are none--car runs perfectly. Can't drive it for the next week or so, but after that I'll see if the light comes back on. If so, I guess cleaning the MAF would be next.