Boost problem on my a3 1.8t

[Letty88]

Hi guys need some help, got a a3 1.8t , having slight boost issues, driving along go to put my foot down as soon as hits boost get juddering noise almost like back firing , had it plugged in as having boost issues , came up firstly with throttle body problem , so took the throttle body off cleaned it put back on and still same problem , changed the throttle body still same problem , did some searching on eBay found someone with same issue and they suggested changing the ignition control module on the airbox done that still got the same problem :( HELLLLLLPPPP, totally out of ideas , if anyone has any words of wisdom be so happy if you could help me