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RE: 1993 S4 Jerk

On 18 Nov 99 at 9:16, Thompson, Scott C. wrote:

> Bob,
> I'm replying to you directly, as I'm not on the Q-list due to the traffic
> volume (a friend forwarded your post.)  I have a 1992 S4 with problems that
> seem very similar to yours.
> When cold, say below 35 degrees F, the car will jerk for the first 20
> minutes or so of driving.  It feels like someone has stabbed the brakes.
> However, my case is farther along than yours.  I will also get throttle
> blips below idle while at traffic lights.  My car also does not care if it
> is accelerating or at constant velocity.  I have had both the dealer and an
> independent mechanic look at the car.  The care does not dump any error
> codes, and here are the things that have been checked:
> Swapped Engine computer
> New Wastegate frequency valve
> New Engine RPM sensor (dealer installed by error - make sure they dump the
> codes with the car running!)
> New engine coolant temp sensor
> New Plugs
> New fuel filter
> coil packs swapped out
> ran BG44k fuel system cleaner through the car
> probably some other stuff checked that I can't remember.
> My next couple steps are to check the Idle compensation valve and maybe the
> fuel pump.  My fuel pump is noisy and the problem may be worse when there is
> little fuel in the tank.  I also seem to have a little boost lag at times.
> Anyway, good luck, and please let me know if you have any success with your
> problem.
> -Scott Thompson

Dear Scott,

Thanks for the interesting note. My case isn't as bad as yours it 
seems, although it probably suggests where I'm headed. At the moment 
the behavior is only at very low temperatures, near or below zero. 

I've also tried a number of things, fewer that you. I am suspicious 
of the ABS system personally.  If I have the car in the garage 
overnight it doesn't exhibit the behavior. This makes me thing 
electronics are the root of this annoying jerk.  I've had a few 
problems with the climate control computer which stopped working at 
low (inside) temps.  I wonder if the ABS controller is temp 
sensitive.  I plan to a) find the damn thing; b) spray it liberally 
with "freeze it" (used to check out temp sensitive electronic 
componets and available at radio shack). I'll report any success to 
the list.