My check engine light had been coming on here and there. I was told by dealer I needed a new catalytic converter. I was also told by one on this site I needed new injectors. The car has always run well and gets good fuel mileage. I changed out the fuel filter, ran BG44K and Chevron Techron through it and that helped, but the light always came back on.
One day I filled up at Conoco/Phillips and noticed the light did not come on. I've been filling up there and no more check engine light. I think I'm on my 3rd or 4th tank full now with no CEL.

 

Could it be your fuel cap seal going bad? Perhaps it was dirty and is now clean?

 

Usually if it has the old style injectors, they need to be replaced 1st, but that BG stuff is usually in a fuel injector kit cleaner, but it works good. good luck.