Lexus employed a thermister based sensor module connected via an airflow tube to the HVAC system.

The sensor is located directly below the ignition lock and is depicted here.

I noticed the climate control was a bit sluggish in adjusting itself, hot or cold, and just never seemed accurate....necessitating constantly fiddling with temperature settings to comfortable lower vs upper interior...

While performing other maintenance, I came across the thermister (resistance changes with temperature) that directs the climate control computer.

The thermister and its uninsulated leads were covered with 18 years of dust which partially explained the problem....along with use and age-related degradation.

I elected to replace mine for $25 from Lexus, but as the thermister element appears to be a clear glass bead, it might respond well to cleaning gently with a Q-tip...not sure to recommend any cleaner such as alcohol...

The climate control behaves much better after replacement... The small plastic square grille covers the thermister. I removed my lower dash cover to access mine...but if you just want to clean it....then if you have a fine bladed tool, the lances for the tiny cover are located top and bottom...make sure you can obtain a replacement in your interior color before you break it...
The thermister bud located inside the assembly..
It appears easy to clean.
Side view of the assembly...the seal is shot and this could have contributed to the problem because it appears air intakes into the grille, so it was likely drawing air from behind the dash instead.
This image depicts considerable dust in the thermister sensor tube that connects via a rubber tube to the HVAC venting...
Toyota P.N...

 

what about taking some canned air to it to dislodge the dust, would that be adequate?

 

Compressed air may work but it may not dislodge everything on the thermister bud surface...then it is a matter of using too much pressure by those contemplating using a 125 PSI shop compressor nozzle...

Also...the seal is likely taken a compression set and not doing its job so that has to be addressed (this comment based on it is an intake and in the event of leakage is drawing air temperature sample from behind(inside) dash instead of in front passenger compartment)

Plenty of discussion about degradation of resistive element in engine coolant temperature sensor over time and use, although it has a harder life residing in coolant, it is possible the same occurs to the climate control thermister...

I am simply reporting findings in my situation.

 

Just today I noticed that my 2000 LS400 has temp issues. Started today.
I set the temp (not auto) up to 28 and the air is cool.
Above 29 and it's warm but not hot.
at HOT it's hot.

If I click auto (temp), at anything below 29 or so (these are Celsius), it turns the AC on AND cold air blows.

Could that be the same sensor issue?

 

^sounds similar to when i left mine unplugged accidentally. did all sorts fo weird things.