2000 Honda Accord

2000 Honda Accord 137,000 miles - recent tune up with new plugs, timing belt, water pump - the works because I'd like to drive it 'till around 200,000 miles. Regular oil changes (fully synthetic oil) and detailed maintenance record. The check-engine light has been on for about the last 20,000 miles, and no shop can find a problem. I got in the car after work today, put it in drive, and it moved, but it didn't really have any power. I noticed the shift indicator light was blinking. I was able to limp it home (about 2 miles). Later I got in to limp it to the mechanic, and everything worked perfect. No blinking light, full power. I checked the transmission fluid, and that's OK. I'm open to ideas! Thanks!