I have an 07 IS250, and have had the problem a couple of times. Just within this past month, it has happened 3 or 4 times, and 2 times within one day. the idling speed drops below 500rpm, and then it feels as if its going to stall on you correct? I called the dealer a couple of times and they said that they don't know what the problem is, and if i wanted them to look at it, i would have to re-produce the incident. which is impossible.