Re: ISV questions

[Huw Powell <human@nh.ultranet.com>]

> What sort of voltage/current/signal should an ISV get?
> I've been playing around tonight trying to get the coupe to idle a bit
> better. The ISV supply hovers around 3.5 - 4 volts and the unit doesn't make
> any difference if it's powered or not. 

Hmmm, I'm a bit new to this but I'll shoot off anyway.  I am gonna
assume you have the three wire ISV, cause I feel like it.

Just had mine off for cleaning (like it wasn;t already) and
investigation.  The center pin delivers 12v.  Each side pin, when
grounded, either opens the valve wide or closes it (rest is about a 20%
open valve).

I would guess that the way the ecu controls it is through the grounds -
typical Audi fashion.

Your 3.5-4 volts sounds like one problem.

There should also be an ISV duty cycle test point (looks like the old
Frq Valve duty cycle test point) hanging by the strut housing area. 
Runs in the 90% range when cold, should be set to about 28% at warm idle
with some stuff disconnected.

As I recall from my schematic, one of the ISV pins is a slave to the AC
circuitry so maybe the "close" ground is not even ecu controlled?  Dunno
there.

I think the bottom line on these things is to give them a good cleaning
and pray to the supernatural forces of your choice.  

One reaosn you may be measuring 3.5-4 volts is that could be 12 v at a
30% or so duty cycle and your meter can;t catch up?

-- 
Huw Powell

http://www.humanspeakers.com/audi/

82 Audi Coupe; 84 4kq; 85 Coupe GT