[200q20v] Great Acceleration until "Brick Wall"

[hah at srv.net]

>Oh wise ones...
>While on a modest 100+ mile trip I encountered several instances while
>accelerating of "bucking, erratic engine behavior".  This happened both
>during "hard" acceleration and occasionally when the cruise control
>would attempt to adjust the speed (appx 85 mph, 22 mpg).  The engine
>compartment fuel filter has about 5K on it and about 120K on the
>engine/vehicle.  I usually run 93 octane and suspect the fuel pump (gas
>tank).  No other symptoms of engine problems.  Are there any other
>filters that may be restricting fuel flow?

I had a severe bucking problem after filling up with 91 octane (the 
"premium" available at that altitude) that I strongly suspect was crap 
(technical term). This was pre-chip, first time after I filled up that I 
exceeded 1.4 bar on the dash gauge - huge bucking, I thought fuel 
filter/pump too. No, just extreme detonation, very very bad. No problems 
the rest of the tank as long as I was very unleaded with the right foot - 
and I was! Probably illegal to so badly underperform advertised octane 
rating, but it was all the way across the state and I seem to have escaped 
without permanent damamge...

If the bucking isn't so severe, it could be a sign that the mass air flow 
sensor (hot wire) has died (or the Motronic thinks so) and you are 
operating on best-guess limp-home mode. Others have documented this in the 
archives...

HTH
Henry Harper
http://www.srv.net/~hah
1991 200 quattro, 112k, picky eater
1988 GTI 16v, 218k, happy with regular
Henry