1991 Chevy K2500 w/ 350 TBI and 4L80E (motor vin K). It is definitely running rich, my engine temp gauge quit working after I bought it, but it had the check engine light already stuck on when I bought it. I get codes 34 and 45 and found this: I'm guessing the code 45 is a result of the problem causing the first one... but any idea's on how to start the troubleshooting on this? I know the Map sensor has been replaced already by the dealership. The truck sat for some period of time with a bad heater core before being used as a trade in there.