I know a lot of people just disable the system which captures heated manifold air and sends it into the aircleaner, especially if only driven in warmer climates.
I can say, without a doubt that it affects highway fuel economy on my 1989 B250 when it is disabled.
While coolest possible air intake is desirable when max power is required, that is not true when at 1950rpm at 65mph driving across country.
I found my system operating improperly. The door that blocks fresh air from infront of radiator was always closed, allowing the engine to suck in only heated manifold air.
The temp sensor modulates vaccuum to the modulator which lifts and lowers the door. There is a Bimetal spring pushing on a pintle. When the spring heats it allows the pintle to drop and less vacccuum reaches the vaccuum modulator and the door drops.
This system is designed to quickly attain keep a ~100F air intake charge, and the engine computer is expecting this. When I disabled mine My normally expected 15.5mpg dropped to just barely 14. I was driving across country and propped the door open 5/8" or so and in warmer temps was able to get as high as 17.4 mpg.
Anyway I bought a Carter TC13 for 18$ on Ebay, as the new old stock part I found was 30$ with 40$ shipping.
They appear identical. I opened up my old one to see how it worked. The brass nipple which sticks up into the air cleaner can be screwed in or out to dial in the temperature. Inward raises temperature. The Pintle on mine was stuck so full vacuum always reached the modulator and lifted the door in air cleaner snout cutting off all fresh air always, I dont know for how long, but I will assume since I was never able to get much above 15mpg for the last 3 years.
I Believe the pintle could have been freed up without opening up the sensor. Mine gets restuck as soon as th espring slams it home. I've not played with it much, yet.
I cleaned the interior of the older sensor with T-tips and rubbing alcohol.
What I thought might have been a soft stick O ring, was just 31 years of coagulated grime which made it through the filter, likely made worse by the K&N oil I used on the filter, when I used to use that filter, before I noticed the inside of the throttle body all dusty.
I drilled a small hole in the aircleaner housing near the sensor, installed A rubber grommett and rtv's the base of it. i intend to stick a K type thermocouple through the grommett and see what temperature is allowed.
One can see how screwing the brass snout in or out will affect how much the pintle drops and how much air is allowed inside to negate some of the vaccuum sent to the actuator which lifts or lower the blend door.
Drove 20 some miles today watching temperature display regularly with this carter TC13 air cleaner temperature sensor installed.
The temperature inside the air cleaner, as read by this thermocouple, once the engine was at full temperature, ranged from 89f to as high as 129f, though it only hit 129f once and very briefly before dropping quickly.
The usual range was 94.5 to 109f at light throttle, and it always seemed to be rising or falling while moving, even at the same throttle and speed.
The only time it seemed to be stable was when parked with transmission in park or in neutral. Stopped in drive at a redlight, foot on the brake, and it still rose and fell regularly. I will estimate the overall average temperature that I noticed would be about 102.5 degrees F.
When accelerating with ~ 1/2 available throttle, temperature would quickly drop to about 19f over ambient (70f), and then once returned to light throttle once at speed, would quickly rise to 112f then lower and bounce around the 102 f area +/-5 degrees f.
I'll return the cleaned original sensor to this location, and capture some data from it as well, one of these days.