^^THIS^^ Had a guy (slim4ages) bring one to me at home with the same issue, cooling system and ICV was all good, no air locks, Idled up to 3000rpm with the map sensor plugged in, unplug it and it was fine.
I ended up putting my ecu into his and it did the same thing (FARK) so we swapped his back in, I ended up just doing a diagnostic and ECU reset on his and the problem went away.
Do a reset and see what happens, use number 2 in 'my personal addition' http://www.rollaclub.com/faq/index.php?title=Series:A/Model/AE80/82/4age_Diagnostic_System
To this day I am still stumped as to why mine did the same thing but ran fine in mine, I doubt that resetting the ecu resets the toyota sensors aswell.
Fixed.