You need new seals for the injectors. Hopefully the injectors themselves aren't leaking. The seals are pretty easy & cheap.

In '89 there wasn't OBD-2 so it's not about your gas cap. I suppose even in '89 you can pull fault codes from the ECM?? Hope someone knows the details for that year. Maybe you peel back the carpet & watch a blinking LED on your ECM.

On newer cars theres a hundred things that can set off your CEL, but the owner's manual seems to say that the gas cap is the only one that mere mortal users can understand.