[s-cars] Hesitation on boost, 95.5 S6

[mswanson at sonitrol.net]

On my recently aquired S6, the car stubles and bucks badly when on boost. 
The feeling is similar to hitting the rev limiter.

Gear doesn't seem to matter nor does throttle position (IE it doesn't only
happen at WOT).  I put the car in 5th at low speed and matted the throttle
and did not get any bucking from the car which leads me to believe it is
boost related.

A quick visual inspection of the engine bay shows nothing obvious.  Hoses
all look fine, etc.  I have a suspision that the problem is fuel related,
since shortly after filling up with a fresh tank of 93 (the car was down
to about 1/4 tank prior to the fillup) the car ran fine for about 10
minutes, including a full boost run through the gears to merge onto the
highway.  Several miles down the road I went to pass a car and the
symptoms started up again.

Other than the short period after the fillup the car seemed to always be
exhibiting the problem during the ride from CT to NY and back.  If I kept
my foot out of heavy throttle it would cruise just fine with no roughness
or stumbling at all from the motor.

Given the symptoms I'm thinking perhaps clogged fuel pump or fuel filter. 
Any fuel pump problems such as this prone to these cars (which is mounted
in-tank, correct?)?

Any input is appreciated.  It appears I'll be out of 'Lurk Mode' now :)


-Marc-
95.5 S6 Avant
87 4ktq
88 90q