[s-cars] S4 bucking under WOT

[Tom Green]

Ivan,

      The "rattlesnake rattle" is the serpentine belt tensioner.  If  
it is the bearing going
bad, then some listers have replaced the bearing by sourcing it  
locally at an industrial
bearing supply house.  Sorry, I have no more information than that.   
The tensioner is
expensive, but can cause some big problems if it locks up or comes  
apart and throws
parts everywhere.  Just the broken belt can do some damage also.

      The WOT bucking should throw some codes but you are strangely  
silent about this.
Give us a break and blink them out or read them if you can.  Your  
description ties the
bucking to high boost levels so any codes should have suggestions in  
Bentley for the
solution.   If you have eliminated most other possibilities, and the  
plug connectors are
old, they could be the problem, but the miss is usually less  
pronounced, i.e. one cylinder
missing instead of all five.

       I think <www.bimmerparts.com>  has about the best price for  
these.

      Sorry I had no time available last trip, but 3 grandsons took  
it all.  I was flogging a
S6 Avant home from Nevada, and it has "needs" also.

      So, where did a Russian learn about rattlesnakes ?  Afghanistan ?

Tom  '95 S6
           '95 S6 Avant





> Ivan writes:

> Same problem keep bugging me. Any time under WOT car would surge  
> violently
> when boost starting to build up. Sometimes it would be just 1-2  
> surges and
> then it accelerate just fine and other time it will surge without  
> letting me
> go fast :)
>
> If I accelerate slowly - car gets up to speed just fine.
>
> It used to be intermittant problem but within last month it started to
> become regular.
>
> What I had done (thanks to advices here):
> 1. Replaced spark plugs
> 2. Replaced air and fuel filters.
> 3. Tested coils using "spark tester" test. All coils tested out  
> fine with
> similar gap. Maybe 1 turn difference.
>
> Yesterday I had to buy compressor (good excuse for wife and  
> starting point
> to collect air tools :)
> Tested intake for leaks today.
> 1. Connected 3' PVC plug to hose from MAF to pressurise all intake.
> 2. Got huge leak from oil cap
> 3. Read archives
> 4. Plug hose to valve cover
> 5. Pressurise again.
> 6. Got very big intake(MAF->Turbo) hose. Yes, it was inflated and  
> ready to
> blow.
> 7. No sign of obvius leaks. Can't really test because was scared of  
> that
> hose to blow up. 10 psi didn't show anything. 15-20psi quick check  
> didn't
> show anything.
>
> What else..
>
> I have that "rattle snake" sound when let off gas. Thought it somewhat
> normal but apparently its not.
>
> When I removed hose from MAF it had some oil in it. Looks like  
> protective
> screen on MAF was wet. Is it normal?
>
> Read archives.
>
> Cleaned up MAF connector. I _think_ it improved a little. But this  
> is not
> for sure.
>
> Anyway. I stuck with what I have and have no idea what to do next.
>
> If it's MAF - then I need to try good one before buying ($$$)
> If it's coils - I'd rather go with 1.8 coils setup.
>
> Anyway - don't want to spend money to replace different parts. I'm  
> sure
> there is better way.
>
> Any pointers on what do I need
>
> Thanks for advice!
>
> Ivan
> 93' S4