I took my 91 runner on a 350mi trip up north this week. It handled everything fine all the way there but the morning after I arrived (cold morning), my check engine light went on. I stopped the car and killed the engine. Restarted and the light disappeared. It then re-lit a minute or two later. I tightened the gas cap (friend suggested) and drove to my friends house, no light appeared. Spent the rest of the weekend hanging out and doing a fair share of driving. No light. Drove back down here to long beach (nice warm day) and right as I turn off for my exit ramp, I get the check engine light. The light resets itself every time I turn off and turn back on the engine. What seems to change is whether or not the light appears.

Any ideas??