Hi chaps need some urgent help with my fiesta rst!

I have just changed the pipe that connects the bottom of the intercooler to the main charge pipe because it split, and now i have full boost again and everythings cool apart from when i try to accellerate on boost about 2500-3500rpm theres a big stutter and all the power is lost, then then the power comes back and so on. Causing a massive kangaroo effect (quite violent). It only started happening when i put this new pipe on!

I dont know if its fuel or electrical releted! the car is standard apart from k&N and magnex.

Please help! has anyone experienced this? any feedback would be greatly appreciated.

Thanks gav,