Toyota 98 Malfunction Indicator Ligt

Hi,
I drive a 98 Toyota Corolla. Has around 91k miles on it. It drives very well. However, today while slowing down on a ramp before entering the Highway I noticed that the engine malfunction indicator light came on for about a minute or so. I drove for another half an hour after that and did not notice the light again. Could this be indicative of anything? Should I wait for some more time before I take it to a mechanic? If I do take it to a mehanic, should I ask him to perform some specific tests?

Also, on another issue, the last time I had my car checked a few months back, I had asked the mechanic whether my car has a timing belt and should I change it and he had mentioned that my car (98, Corlloa) has a timing chain and that lasts a lifetime and that I should not change it. Is this correct?

Will really appreciate your answer.
Thanks