CIS--E-III Idle speed

[Huw Powell]

> Question regarding the idle speed on an Audi 100 with NF engine.

~ 800 rpm.

> I had read somewhere that there is no idle speed adjustment.  Its
> handled entirely by the ECU and Idle stabilizer.  When working
> correctly, once the idle switch goes closed circuit the ISV kicks in
> and regulates the idle. 

Correct.

> Thus if the car occasionally stalls at idle,
> either the ISV is sticking, malfunctioning, or there's a vacuum leak.

Or something else is wrong, but, yes.

> At the same time, I've noticed that there is actually a screw on the
> throttle body for adjusting the idle speed. 

It's a holdover, leftover from previous ancestral species, serves no 
function.

> If I don't use this screw, my car idles great when the weather's
> cold, but once its warm, and the car is warm, it will occasionally
> stall if for example I do a sudden stop.  Its almost as thought the
> ISV doesn't quite have time to do its thing.  Other times, it might
> just about stall with rpm dipping under 500 but then the isv kicks in
> and brings it up to around 700.

Your idle switch might be closig slowly (ie, sticky or dirty), or 
perhaps your ISV takes a few seconds to get working (sticky or 
dirty...), or perhaps something is mistuned and the "default" the ECU 
heads towards first at idle is wrong enough that the correction time is 
evident.  By mistune, I mean either a wrong adjustment *or* vacuum 
leaks, etc.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/