[T3] running rich and mystery material

[Jim Adney]

On 10 Nov 2012 at 7:02, Dave wrote:

> [[[However, a faulty AAR won't make the mixture richer.  It only controls
> the fast idle speed, by reducing manifold vacuum which lets more air and
> hence fuel into the cylinders]]]
>  
> Yes, a AAR doesn't control mixture, but it does provide a means to add air
> into the IAD - resulting in an increased idle speed so the motor does not
> stall out with the cold rich mixture. I'm thinking if VW never installed a
> AAR system on our motors - our cars would choke out from the cold rich
> mixture and probably sound like Dennis's T3 in the morning J.

I don't think this is the right way to think about it. The cold 
mixture is rich because that's what a cold engine needs. The AAR is 
there because there's a lot more friction in a cold engine, which 
slows it down. The AAR keeps the idle speed up so that it doesn't 
stall, as you suggest, but not because the mixture is too rich, but 
because the idle speed would otherwise be too low.

Even a warm engine won't idle well at 500 rpm.

If the only problem was an overly rich mixture when the engine was 
cold, Bosch could easily have altered the amount of cold enrichment 
they designed into the system.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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