Surging effect when cruising on static revs

[Kogi]

Guys,

I have recently remapped my engine with OBDTuning software and installed an open filter from Simota, the guys from my tuning workshop believe that it should gain around 225HP to my LeonFR (2005).

Now I have an interesting problem, turbo surging when surfing on static revs, pay attention (!) it does not happen within accelerating, it goes smooth, but when I raise it to for example to 4000RPM and keep my leg on pedal without pressing it in, trying to cruise on particular revs and speed, I'm starting to feel a surging issue.

It sounds like Im loosing a pressure and getting it back .. weird ...
Maybe its a wastegate valve, but what the reason to do that, I am not overloading my turbo so it should not be any over boost issues and the N249 is not involved so far ...

any clue ?

thanx !!!

 

[CupraUK]

Sounds like a dodgy N75 to me, I had the same problem after my remap. Replaced it and its much better now (still a little bit of surging at low constant throttle but not when giving full beans)

 

[Kogi]

So its like my original N75 is slow and lazy ?

Which vendor would you suggest? either: C or J version ?

thanx !