By you turning the boost down is stopping the ecu from cutting the overboost sooner i should think as the turbo is not boosting as hard.

One thing to check with cutting out idleing when the car is up to running temperature is your oil pressure. Ive had the same problem twice, one turnt out to be a blocked oil scoop, and the second one was big end bearings on their way out causing a big drop in engine pressure, hence the stalling.


And as said above, i would wind the boost valve all the way in until you can get someone to set the car up properly on a rolling road or something. You'd be amazed how much damage can be done by not having it done properly.