Why does 2005 Avalon idle high when cold?

Starts from a standstill were rather******. The mechanic told me that they usually clean the throttle plate at around 100,000 miles. I'm below that, but thought it might help. He had said that, as it's a drive-by-wire, sticky plates arent felt as readily (through the accelerator) as cable controls. My starts actually do seem smoother, but the cold idle is driving me crazy.

Unplug what? The throttle? No.

I didn't actually remove the throttle body, just all the air-cleaner stuff ahead of it. That's all put back together nice and snug, and all the hoses and tubes are tight. As this is drive-by-wire, with no idle air control valve, I'm thinking that, for some reason, the throttle is opening too far when cold. It could be a temperature sensor, but I can't imagine any scenerio where a very cold engine was supposed to idle at 1800RPM. I dread going to the dealer. They'll undoubtedly want to replace things like the throttle control or the ECM. I re-disconnected the battery again overnight to see it something might re-set, but no go.