91' engine light

I have a 1991 Ford Probe. My check engine light originally started to come on in fifth gear at 70 miles per hour. However, it is coming on more frequently and in every gear. It does not stay on and there are no oil leaks or smoke. I had the battery, the alternator and the starter checked, they were all good. I did this because besides the check engine light, after two days the battery was dead like something was sucking the juice from out of it. What can I do? :confused: