What year?
I found a tech. serv. bulletin for cold hard start/driveability on 89 and 90 models. If the complaint was both cold start and driveability, tech was instructed to install an updated ecu. Have to have the 22 deg. Celsius c.s.i ti.me switch, as the improved cold start injector logic was programmed to work with that one only. This was after making sure all mechanical, fuel, and electrical/electronic systems were operating within specifications
Reference: engine number: 024 date 08-31-90.
For cold start ONLY issues, toyota has an improved c.s.i. time switch that changes from 22C(72F) to 45C(113F). they are marked on the hex with either a 22 or 45.
EDIT: this is only for the cold hard start/driveability issue, not the code 12.