If someone found a resolution to the idle speed issue please post.
I have the same issue with my 06 s430. When the dash thermometer reads outside temp of 90 F, and the AC is on my idle rises to about 800rpm. When the temps were at 90 or higher, I sprayed some cool water directly on the temp sensor and watched the temp and the reading on my dash drop.ped to the 70's F. The idle speed dropped to normal. 500rpm - 550rpm. I replaced the ambient temp sensor (only $18 cost) but the issue wasn't resolved.