bucking above 1.1 bar, max boost 1.3

[Chris Covington]

I took a nice trip this weekend to Burlington, VT to visit a friend and
give the 200 a nice 200 mile each-way trip.  No problems on the way there,
in fact I even got 23.8MPG.  On the way back, merging/passing a Volvo
after the I87 onramp in 3rd gear, at around 5K RPMs at WOT the 200
seriously bucked and I let off the throttle.  The engine ran fine as long
as it didn't get over 1.0 bar, without any missing / roughness, then it
would buck really hard as if it were backing off or intentionally
preventing high boost.  I let off boost for awhile then I then pulled over
to get gas and check the intercooler hoses, and everything seemed fine.
After the fill-up on 87 the 200 seemed normal again - I still got 1.7-1.8
but I didn't push it too hard because I was more concerned with getting
back.

When I got home I tested it again and basically now get serious bucking
in any gear starting when boost gets over 1.0 bar, with 1.3 being the
highest I can get.  I thought it might've been the WOT switch because it
seemed to only do it at full throttle, but under further examination it
will buck at 3/4 throttle too, or in any other situation in which it goes
above 1.0 bar.  So it seems to be a boost issue (or the witholding of) of
some kind.  All my hoses are either new / in good shape.
Is this the WGFV?  Something else?

Chris
'91 200q20v