There is a working PWM idle code in the current extra code, but you will essentially need a very large boost controller valve. I think Matt tried this with a boost controller once and noticed that it doesn't have enough throughput. Maybe a nitrous valve would work better...? I've never played with a nitrous system before so I don't know how big they are.

The MS2 has a nice GM stepper motor idle valve controller (very similar to the stock Neon one) chip built in but the code to run it isn't exactly 420A friendly yet. There are a few people scattered about working on converting the extra code but no one with the skill seems to be very interested in doing it. The problem is that the extra code has been written by many people, each person would have to convert their segment to the new C language, or someone/a team would have to learn how the entire program is written. The code is about 13,000 lines of assembly (around 1430 lines compiled) right now. No one wants to deal with that on their own unless they have way too much free time or are being paid to do it.

If you leave the stock ECU hooked up it will really mess with the idle valve especially if you don't have half of the stock sensors attached to it or have resistors on them like me. It kind of sits there, stabilizes, but when you go for a drive it will open and close the valve very quickly attempting to the engine back to idle. It makes driving very unpleasant. If you leave it unhooked, your idle will be slow when the engine is cold and fast when it is hot, and if you throw boost pressure on it the idle valve will be forced open and you will have to plug it back in for a short period of time so that the stock ECU can re-adjust it back. Very annoying.