[T3] my long term issue have to unplug TS1 for a smooth idle.

[Jim Adney]

On 1 Oct 2019 at 10:21, William Jahn wrote:

> Yet you said the AAR open or closed , the mixture should be
> approximately the same. Does this mean it still does have some affect of
> making the mix richer?

Assuming we're leaving the temp sensors out of this, and also assuming that 
the FI pressure sensor and brain are working as PERFECTLY as the 
designers hoped, extra air at idle should not make the mixture leaner or 
richer.

Look at it this way:

Extra air + the right amount of extra fuel = no change in richness.

Less air + the right amount of fuel reduction = no change in richness

> Yet you said " If the idle changes significantly, it means that less
> air is getting thru the AAR. The amount of idle speed change will give
> you an idea of how far the AAR is open." I'm confused because I find
> the more air through the AAR there is is when I see the idle change the
> most. 

Yes, I think we may be saying the same thing. I'm just trying to get you to do 
the testing in an easier, and more informative way. Pulling off the hose 
between the AAR and the IAD is not something you should do while the 
engine is running, so it doesn't tell you anything about how the AAR is 
changing during warmup.  

If you use your thumb, while the engine is running, to see if closing off any 
air thru the AAR changes the idle speed. You can do this calmly and 
non-destructively while the engine is idling. This is a functional test, looking 
only at what effect the AAR is having. It does not rely on anything related to 
how the AAR works or what it looks like inside. As such, it may not satisify 
ones curiosity about what's going on in there, but it answers the question of 
whether it's working right or not.

If closing that hose causes no change in idle speed, the AAR is closed.

If closing that hose causes a small change in idle speed, the AAR is partly 
open.

If closing that hose causes a large change in idle speed, the AAR may be 
fully open.

>  I can see why the Idle air screw does not change the mix yet it is a path
> around the closed throttle valve where the AAR is also a path around the
> throttle valve , it's just a different path that slowly reduces as the
> valve closes until it becomes no path , both past a closed throttle plate.
> The idle air screw is fixed once it is adjusted for proper idle speed ,
> once it is set then it still passes air and the same amount whether the AAR
> is open or closed

This is all correct.

> the AAR is simply additional air needed because of a cold engine with a
> richer mix because of the TS2  needs more air to run and because of
> cold thicker oil , it this what you are saying? . 

I suspect the problem here is that you're equating more fuel with a richer 
mixture. That's not what richer means. Richer means an increase in the ratio 
of fuel to air. The goal of the D-jet system is to keep that ratio constant, as 
long as the other operating conditions remain the same. It may not succeed, 
but that's what it's trying to do. [I'm talking about idle here.]

That's not to say that the D-jet FI tries to keep the ratio constant under all 
conditions. Part of its design is to alter the richness (ratio) depending on 
need. It's probably richer under load, and we know that it's richer when cold. 
How does it change with RPM? I don't know, but the Bosch folks who 
designed it probably had something specific in mind.

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