I bought a 87 Iroc with a 350 TPI, and it has this trouble code. What is it, and how do I fix it?

 

Code 23 is:
MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)

How to trouble shoot:

1)Disconnect MAT Sensor.
1a)Ignition "ON", Engine stopped.
1b)Check voltage between MAT sensor harness terminals with
a multimeter.
1c)Did you get "4 volts or more" or "Below 4 volts"
2)Below 4 volts
2a)Check voltage between harness connector signal circuit
and ground. Did you get 4 volts or more, or below 4 volts??
2a)Below 4 volts, "open signal circuit", "Faulty connection",
or "Faulty ECM"
2a)4 volts or more, "Faulty sensor ground", "Faulty connection",
or "Faulty ECM".
2b)4 volts or more
2b)Check resistance across MAT sensor terminals. Should be less
than 25,000 OHMS. Is it??
2b)NO, Replace sensor
2b)YES, Check for signal circuit being shorted to voltage. If not
shorted to voltage, code 23 is intermittent.

MAT Sensor Signal "Ckt 472" (Tan wire) (C12 @ ECM)
MAT Sensor Ground "Ckt. 452" (Black wire) (D2 @ ECM)

Hope this helps you!!!