Can what appears to be a leaky interface in the factory upper intercooler pipe cause the GMTU boost (normally ~23 PSI) to be reduced to 15-17 PSI? I performed a boost leak test at around 15 PSI and clearly had soapy bubbles all the way around where the two sections of the pipe come together (where red arrow pointing in image). Doesn't seem like enough of a leak to cause a 5-6 PSI reduction in boost, but maybe it is.

 

Any leak in the piping should be repaired before going forward with your boost loss search.
Is it enough of a leak to cause that much boost loss ? I doubt it but the computer may be detecting a problem and "backing off" the pressure.

 

It's a boost leak, but it's also a loss of metered air.