[TonyS9]

You are correct in the assumption that the idle valve can't react quickly. Actually its more the ECU software, the valve itself is normally very fast, fast enough to deal with engaging the automatic drive or several kW of AC provided said loads are signaled to the ECU at the same time.

If you let the clutch out without using the accelerator you can get a better sense of its reaction speed (very slow). Its really just for for the big loads and maybe a little compensation for the lights and other heaters.

Revs dropping are usually because the air flow is too high with a low signal from the MAF or just too low. This can happen after boost without any dump (as you have found in the archives) and if the throttle body is either blocking the idle air (deposites blocking) or allowing too much of it (lumps preventing closing).

No dump will definately stall it, but if you keep reving it up while it depressuries over a few seconds will eventually idle. Its just the throttle closed signal makes it go into a much leaner closed loop mode than open throttle open loop mode. Disconnecting the the throttle closed switch can stop it stalling, but it will run badly for other reasons then.

The dirty throttle body problem is normally related only to fresh start, I think the ECU remembers the idle point after that, not 100% sure. But do check it off the car, it should be spotless, and that all the little holes are clear. It can be hard to see them all.

You could have a slight air leak or low fuel pressure if its doing it all the time.

You should be able to close off the idle air by squeezing the pipe, it should idle / nearly stall at 500rpm then.

You might be able to infer certain things based on the fact the lambda light isn't coming on, but this can take a while before it gives up. A voltmeter or narrow band O2 meter will give a better indication.