I have posted this problem before with my SES light going on intermittingly and it has gotten better as where the light comes on then goes off. The car runs fine was running a little rough after I changed some items listed, but then checked the air filter and it had many acorns and must have been taken over by mice prior to my ownership. It's one item I never checked and once it was replaced, I could tell the difference, but the SES light continues to come on. I have changed the following items since about 2 years of ownership.
Idle air control valve, Throttle position sensor, both O2 sensors, air filter, fuel filter, Injectors, sparkplugs, cleaned the throttle body, sent the ECM out and there were no problems thinking it may have been sending a code when there was no problem.
I have an OBD1 reader and it gave me a 44 code that is right bank 02 sensor running lean. After the 02 sensors were changed still gave the same code so that when I sent the ECM out to be checked and it was fine. I think I am going to change the 02 sensors again they are cheap enough with a 1993 only having two sensors. I am also going to start checking vacuum lines the car is 31 years old with 58k on it. I'm also thinking to replace the EGR and the Manifold Air Intake air temp sensor. Any other ideas I may have overlooked.

 

It could be a vacuum leak or an exhaust leak.