jetta's first problem

[jbrandow@webtv.net (Jeremy Brandow)]

  I have noticed my first problem with my Jetta in over 40k miles.  I am
just wondering if any of you have experienced something like it.  
  I let my glx Jetta sit overnight as usual.  After starting it in the
morning I let it warm up for 30 seconds or so, this is routine. If I
then drive my jetta without flooring it until it is warmed up I don't
have any problems.  Where the problem happens is if I floor it before
it's warm. (half way to normal temperature), my car bogs down after
about 3-5 seconds of full throttle.  Once the engine warms up the
problem is gone.  Sometimes if it bogs enough, my check engine light
comes on, but eventually by the end of the day it's back off.  My jetta
does this regardless of weather temperature.  I usually avoid the
problem, but it is annoying anyway.  
  I was thinking that maybe I have a bad O2 sensor or maybe a fouling
plug?  I'm really dreading to take it to the dealer.  I don't want to
hear what they are going to say about my performance mods.  
  Jeremy Brandow
98 JETTA GLX Tornado red
Q-chip, Neuspeed anti roll bar, abd intake, AWE short throw shifter,
shocks and springs to come!