On some of the pictures posted, I see 3 available modes for the interior ventilation (the right most HVAC control button): fresh air, recirc, and auto. In the interior photo inside Lexus's sales brochure, I see the same button without the auto option. Was the one with auto mode an IS350, and the one without a 250? Also, what is that button between the off button and the windshield defroster?

 

I don't have an IS, but if I remember right from my reading the 250 has a two position switch (in/out air) and the 350 has a three position switch (in/auto/out). I assume your question is about the auto position and I think that is a smog sensor for selecting in and out air.

 

Auto mode for the IS350 controls the smog sensors. When certain amount of particulates is detected, the system will automatically close the vents from FRESH to RECIRC. This is only available for the IS350 base to the fully loaded model.

 

Also I believe there are 6 levels of sensitivity you can set the auto level.

How to set the sensitivity of the air intake control in Auto mode (350)?
1. Press the Auto recirculate button for >2 seconds.
2. Inc/Dec the Temp switch from -3 (Low) to +3 (High) or 1(Low) to 6(High) [Navi]