I just rebuilt the engine on this 2002 B6. New cylinder head and intake camshaft. Problem im having with the car now is that it wont hold boot. It boosts to around 5 psi and then will drop off to 0 psi around 3700-4000 rpm.

Any suggestions on what to check?? ive done a leak down test at the intake and dont find any leaks

 

80 views and not one bit of insight?

 

im having a similar problem, but i didnt rebuild my engine though (100k this weekend). When I turn on my AC my turbo gets held back at 4 rpm too. and its causing high pressure (problem #1) pretty much everywhere like my gas tank and AC pipes. I was worried about it being the aluminum blow off valve causing the mixture to be to gas rich (problem #2), but ur case kinda nullifies that. Im starting to think I need to override the mixture programming cause my car was driving very clean.
hope this kinda helps