Hiccups under boost...

[AUDIDUDI@delphi.com]

For the last month or so, I've been chasing an intermittent problem with my
'89 200q.  On occasion, the car won't run cleanly at greater-than-OEM boost
levels: It pulls fine up to 1.3 or 1.4 bar (per the OEM gauge) then hiccups
and bucks as if it was missing or had a tank of bad gas.  Other times, even
just a few minutes later, it pulls fine all the way to 1.8 or 1.9 bar...

The ECU is totally stock, the increased boost being achieved with a stiffer
spring in the wastegate, and the knock-sensor indicator on the dash doesn't
light up, which suggests it's not a timing problem.  It happened again this
afternoon for a few minutes but didn't happen after the car had been parked
for a while.  I thought it might be heat-related -- it hit 107 here per the
climate control thermometer -- but it was 105 when it was working okay so I
think that's not it.  I've checked the diagnostics for fault codes but came
up empty-handed.  BTW, my car is an 89.5 with dual knock-sensors and I have
recently replaced the cap/rotor/plugs/wires with OEM Bosch parts as well as
installed a K&N air filter, for what that's worth.  Otherwise, it's a stock
car w/100k on it...

Does anyone have any clues or suggestions for me?  It runs just fine as the
factory intended but I don't want to go back -- No, make that CAN'T go back
(you know what's said about power and corruption!) -- and since I'm waiting
until the problem has been solved before installing the RS2 turbo and other
go-fast goodies I bought over the past few months, it should be clear why I
am anxious to find a cure for this and quickly...
 
     _             _             
    / l       l o l  \       l o   Jeffrey Goggin
   /__l l l / l l l  l l l / l l   * * * * * * *
  /   l l_l \_l l l__/ l_l \_l l   AudiDudi@delphi.com