Any way to adjust outside air temp reading?

Depends on how "rapidly".
The thermistors used in most automobiles have a fairly long time constant, so if you see it shifting rapidly by 15-degrees or more then yours might be getting a little dodgy.
Thermal Time Constant and NTC Thermistors: A Practical Study

 

I will have to do more driving to confirm this. But the changes I saw were within 40 min of drive less than 20miles. The temperature display went up and down as I drove 30mph. Once at my driveway, it was not changing anymore. That being said, the actual air temperature in our region can vary vastly by microclimate differences. It is fairly common to see a temperature difference of more than 10 degrees in my town and town next to us less than 20 miles away. And even at the same spot, daily fluctuation of more than 30F is fairly common.

The graph is from the thermometer reading of outside of my house on the day I noticed this wild fluctuation in my car.

 

That looks fine to me...FWIW.
Seeing 15-degree temp swings within the same number of seconds would be more suspicious.

"Rapidly" means different things to different people.

 

Put a piece of tape next to the display that says subject two degrees for actual temp.
You know this is what is needed but the tape it for anyone else who pilots your car so they get an accurate indication

Mike

 

Good question, but not as tricky as you might expect. I use a Fluke IR thermometer calibrated against a name brand sous vide circulator,, which allows me to measure the temp at something other than freezing or boiling. Use a container with the same emissivity as your thermometer is set for, full it with water, bring it up to temp, measure. My Joule and Fluke reliably read the same temp. You can also do this with a probe thermometer, of course. This isn't perfect, but it will let you know if your thermometer is way off base. And it works better with reliable name brand products. I recommend Fluke (formerly Raytek) and ThermoWorks products, but there are other good brands out there.

 

That's what led me to this thread. At 1PM, parked in the sun, mine still shows the 46°F that it showed when I parked it in a parking garage last night. It showed the same temp when I checked at noon. So I drove it out into the sun. My cheap Chinese crap thermometer says it's in the 70s in the shade, but the car still thinks it's 46.

 

Mine shows the same temperature when i start as when I parked, then takes a long time to adjust