03 a4 1.8t boost trouble

my 03 a4 1.8t quattro with the following mods apr stage 1, 3" test pipe with non foulers installed 2.5"down pipe back exhaust and k&n cone filter heres my problem my cel came on after a road trip po441 code is what pops up evapritive emission system purge flow incorrect. i dont know what that means is it my factory d.v?? now will that couse my boost to drop in the high end of third and all of fourth it studders like its cuting out but it has brand new coil packs. i can also watch my boost drop from 17.5- 7psi if you can help please write me