1995 mighty max - check engine light turns on and off while driving

Hey I just got a 1995 mighty max. I passed the California smog test the other day but now my check engine light turns on for a few miles than back off for a few miles. If I turn off the truck when the light is on, it's still on whenever I restart the truck. But, it will turn off after I drive a bit. It doesn't seem to come on when just idling. Any ideas about what might be happening? I don't have the manuals yet... hopefully today I'll get them and also a multimeter to check the ecu codes. Thanks yall.

Has the ECU been rebuilt yet? 2.4s are notorious for the flaky ECU that starts causing random electrical system shorts and cutouts after the capacitors start leaking and the solder joints crack after so many heat cycles of expansion and contraction.

Crack open the passenger side kick panel and pop open the ECU. Inspect the caps and see if any are bulging or leaking. Take a whiff of the circuit board. If it smells at all fishy or metallic, you have a bad ECU.