http://www.cygnusx1.net/Supra/TechTi...ror_codes.aspx
the black box is sort of hard to break unless one goes dicking with it.. trying to "clean" it's optics by spraying something in there and wiping it off.. most likely cause is a faulty wire. I'd start there.
helping to rule things out.. your ecu is not the culprit.. those things don't generally break.. So that just leaves.. your afm. or your afm circuit.. the box or its wires.. check the voltage and you have your answer