need some opinions with boost surging.

[a4nub]

my friend has an a4 with a 1.8t motor which has the following mods done. - autobahn88 FMIC - looks like to be a cheap ebay atmo BOV - ball and spring type turbosmart mbc that has bypassed the n75 valve completely. - K&N pod filter. the car was running like new for a couple days after he bought it then the boost started surging under load but the boost gauge was still reading 15psi(what the mbc was set at when he bought it) but felt like nothing. i disconnected the mbc and ran a straight line from the actuator to the turbo and it is running 2-3psi without hesitation. he is comming over tomorrow so i can fit the stock air box back in and replace the BoV with the standard DV. does anyone have an idea what might have caused the surge? boost leak? is it posible if all vac hoses are intact that the cheap Bov could be faulty and leaking air. will test the maf tomorrow aswell and connect the n75 up without any mbc and see what the result is.. if anyone has any other suggestions please shoot. the traction control light is on but the audi dealership says it would not be related to the boost problem. i have searched the forum but it is hard to find the right information when i am very new to this.