How about the MAT (manifold air temperature) sensor?
Only used in 305/4.3 applications and it's output signal to the ECM is directly dependent on ambient air temp.
Thing is - if it's malfunctioning, a 23/25 code will be set. But, you didn't mention any MIL or DTC 's.
Anyways, I'd check the sensor's resistance as a function of temperature using the charts below.
Location:
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Low error - DTC 23:
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High error - DTC 25:
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