After finally figuring out where my fuel leak was(line going into FPR base not pushed in far enough) I am now showing a code 23. MAT sensor. I unplugged it numerous times removing the plenum to get at the AFPR. This morning I stuck a screw driver in there and jiggled it around the best I could, no it's not loose. When I started the car the light was off. I drove around for a while and it came back on. Yes, I did reset the ECM, unplugged the - terminal while putting on my Hooker exhaust. Any ideas anyone? Thanks.
Unfortunately, you might be removing the plenum one more time. You should check the MAT sensor resistance and wiring harness. You can compare the resistance at a known/presumed temperature to the chart:
If the sensor resistance is good, you need to meter the ground wire at the sensor harnes for continuity, and meter the sense wire for 5VDC without the sensor connected. If those are O.K., you may have an intermittent connection at the ground or ECM. You may also have an intermittent MAT, and a replacement sensor is a whole $8-9. The PITA will be removing the plenum again, for sure.
EDIT: Since you have a Pontiac, I suppose you could leave the plenum in place and relocate the MAT sensor, like I did: MAT Sensor Relocation.pdf
If the sensor resistance is good, you need to meter the ground wire at the sensor harnes for continuity, and meter the sense wire for 5VDC without the sensor connected. If those are O.K., you may have an intermittent connection at the ground or ECM. You may also have an intermittent MAT, and a replacement sensor is a whole $8-9. The PITA will be removing the plenum again, for sure.
EDIT: Since you have a Pontiac, I suppose you could leave the plenum in place and relocate the MAT sensor, like I did: MAT Sensor Relocation.pdf