S6 "sputtering" puzzle

[Tihol Tiholov]

> ... the car  still "sputters" at WOT and full boost. It doesn't buck or
cut out it just  sputters. If I peddle it to maintain below 17 it pulls like
a train. Go to  WOT and 20 or above PSI and she sputters badly. Prior to all
this it was  running 27 full boost very nicely.
I have pressure checked it twice with a stethoscope very methodically  and
it
holds pressure even after I take the regulator off. It also  blinks no
codes.
Any usual culprits for such misbehavior?

 vwvortex dot com says sparkplugs or ign. coils, when CEL blinks.
I'd add ign. wires, MAF and/or bypass valve based on the same intermittent
issue with an 1.8T, when I gun it under 2500 in most gears.