Mine does the same exact thing in hot weather. I took it into the Isuzu dealership and they told me that it's caused by a "Master Flow Sensor" which needs to be replaced for $150 and $47 Labor (Courtesy Acura/Isuzu, near Denver, Colorado). I personally think they're lying, so I'm going to take it into a truck place by my house for a second opinion, but I'll let you know where this leads. Same exact symptoms, though:

All only occur in hot weather (85 degrees +)
1. At low RPMs/speed, AC blows hot air which cools down as I get the engine revving or speed up.
2. Starting the VX, it either dies or I have to mash the gas pedal to get it to stay started.
3. Once started, the idle is either extremely high (2500+) or extremely low (in the 100's), and almost dies. If the idle is high, the vehicle behaves like an over-excited husky-- MUSH!