[T3] Bad day at the (FI) office

[Jim Adney]

On 31 Mar 2016 at 18:35, Daniel Nohejl wrote:

> In other news, we´ve developed a hunt at idle. I started noticing it
> either yesterday or the day before and today it was even more
> apparent, especially once the motor was fully warm on this nice 70*
> day. It´s not quite as regular/rythmic as hunts we´ve had in the past,
> but it´s quite noticeable with swings of around 100 rpm so itTMd run
> down to 820?rpm and up to 920 rpm where we set the the idle on Sunday.
> I pulled the hose from the oil bath to the AAR off of the oil bath and
> put my thumb over the end. There was quite a bit of suctio?, but
> instead of my thumb over the end mak?ng the idle stabilize, it ?till
> hunted. However, the overall idle speed dipped about 100 rpm lower ?o
> the hunt was now 750 rpm to 850rpm. 

That sounds pretty normal for D-jet, and the AAR is mostly closed. I 
don't see a problem here. There's no real idle stabilization in the 
D-jet, so the idle is never as steady as in later cars. It may get a 
bit better as you get things dialed in closer, because it sounds like 
the brain might be playing with the richness a bit, to keep the idle 
from dropping too low.

I always adjust the idle with my thumb over that hose. That way it's 
right when the AAR is fully closed. Your idle is adjusted a bit low, 
which makes the D-jet struggle when the idle falls below what it's 
expecting.

> Clearly, the AAR is suddenly not closing all the way, but there´s
> still a vac leak somewhere. 

Nothing here suggests a vacuum leak. A small vacuum leak would not 
cause hunting; it would cause a slightly increased idle speed. Signs 
of a vacuum leak would be an idle that you can't adjust down to the 
right rpm. The really big loping is a sign that the idle is adjusted 
way high or that there's a really big vacuum leak, or a small vacuum 
leak combined with a misadjusted idle.

> Also, as an aside, I noted that with the resistor off of the CHTS, I
> had only 59 ohms of resistance and 162 with the resistor back on. If
> it´s only 70* and it´s reading that low, isn´t it fairly safe to
> assume that on even hotter days it would drop even lower? 

Sure, but not much.

> As another aside, we just got an electric AAR in the mail the other
> day. It was cheap and we ordered it months ago after we realized we
> had a D rather than O shaped hole in the case. It took just about
> forever to arrive from Canada. Anyway, are these known to be any more
> reliable with fully closing than the purely mechanical ones? 

The electrically heated AAR was used on '70 and later AT cars. 
There's no advantage to it, and it's not repairable and not 
adjustable. Plus, you don't have the wire from the fuel pump relay 
that it needs. Polish it up and put it on your favorite display 
shelf.


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