Check the idle position switch setting. When the throttle is closed and almost gets to the fully closed position the i.p.s is activated .
This takes the management out of the "running" mode and places it into "idling" mode.
The idling circuit is completely void and separate from the normal running mode.
It may be that the switch is adjusted so that it activates too late and the engine cannot recover enough to idle.
It may also be that the switch is faulty. Un plug it and see what happens. If the engine idles reasonably start looking for another i.p.s.
Can some one tell me whether the switch is resistive or is it a mechanical switch ?