94 Camry error code 12

I have been trying to trouble shoot the Error Code 12 on my 1994 Camry 4 cyl. So far, I have no clue. I have checked all of the sensor connectors I can find. I have reset the computer by removing the efi fuse and disconnecting the battery. Each time, the light stays off for about 2 minutes and comes back on, before I can even get out of the driveway. It is an automatic. The speedometer and tachometer both function. It runs good. I need to get safety and emissions done. Not sure what to do.