Lack of VR6 power?

[VWnut]

My mate recently bought a VR6 on an L plate. The problem is that it is lacking a lot of power, it's a joke. He has an induction kit, cat by-pass, full magnex exhaust. He took it down to VW who diagnosed a few defects which were sorted (including the coil pack). The car still has a serious lack of power even with all of this done.
The car doesn't pick up smoothly at all and seems to lose even more power the higher up the revs you go.
Has anybody experienced this or have any idea what could cause it? Could it be the mods he has done?
Cheers
Tom

[golfvr6]

Does anything show up on the fault code reader?
could be timing is out, has the head been off?
other suspects are airflow meter and oyxgen sensor.
If it has a cat bypass pipe then is the oxygen sensor in properly?

[VWnut]

Could well be the timing, the fault code reader did show up a faulty oxygen sensor. this was replaced along with the airflow meter.