Found some slight green on the female connector ECU harness, cleaned with some deoxit D5, cleared the codes and did throttle adp.
Drove it for a bit and problems seem to be gone, for now at least, fingers crossed.
PO did mention something about water in ECU before and the box was missing the two rear screws, the insides of the box looked really clean, no signs of water or corrosion on any of the relays, put some Vaseline on the rubber gasket ECU top cover, reinstalled the cover and replaced the missing cover screws.

Also ordered some deoxit d100 in spray form in case this problem comes back again.