Boost Problems

[downlowdubs]

I'm not sure if I'm posting in the right place but I need help diagnosing a boost problem.

Vehicle: '04 GTI 1.8T

Engine mods:
APR Chip (stock & 93 octane)
2.5" Techtonics Turbo Back with Borla Muffler
2.5" ABD Cold Air Intake
Forge 007 Diverter

I have been driving the car in chipped mode for years now and never had any problems. Recently, at peak boost(~19psi), the boost pressure stutters (like a machine gun) then the car goes into limp mode. Shooting in the dark I tried changing the spark plugs and this had no affect. The last time I was at the dealership they said I was showing an Overboost code when they did a diagnostics check. So I switched the CPU and have been driving in stock mode for the last few weeks. Now, at peak boost (~10psi), the car does the same thing and goes into limp mode. Even in limp at peak boost (~5psi) it still happens.

Any ideas?

[Pejman]

If I remember correctly....

Check out your diverter valve, make sure it's clean and the spring in there is in good shape...

Do you have a N75 valve installed?

[downlowdubs]

I just cleaned and re-greased the diverter about a month ago. I just read a post on another site about the N75 valve. I still have the stock one. I will look into that. I think I have an MBC laying around somewhere. Maybe I can try to install that first. Thanks.

[the dubshow]

Sounds like a youre hitting soft limp mode. Research over boost kits. But essentially, you loop a MBC before the n75 valve so it doesn't ever get more than 18-20 psi.