well not actally have heard the car, if the pug gap is to big, ie the stock 1.1mm and the coild are a bit week, the denser air causes the coil to work harder and you get a brake down of spark. This happend to me, i had to go all the way down to 0.6mm just to idle, and .55mm to run.
The problem is you can't regam platnums to easily, or arn't suppose to. go out and buy a copper set, the shop will know which ones, and buy the ones that are gapped to 0.8mm. Put these in and see how it goes. It is most propably the spar.
If it is hitting R&R, which i unliky, if you are running stock boost, then you may need an SAFC II air flow computer or a full computer to fix it. The ecu detect that there is to much air comming into the engine, and retards the ignitions and hence limits the boost.
Hope that helps