I recently bought a 2006 Taurus SEL. The car has functioned as designed however recently, sometimes when the rpms go low, like slowing down for a stop sign, it will die. Or, if going down the road at high speed and turn the AC on, it will die. In either situation, there are no weird noises, struggling, it's as if the car just decided to turn off.

I had the battery checked today and alternator, I was told they were both good.
I am considering an idle issue (maybe start with changing the IAC sensor) and I know that the O2 sensor has not been changed (car has 100,000 miles).

Thank you,
Michael