ISV has me puzzled!

[Huw Powell]

> on my 874kq Just doing some random checks to see why i'm having cold start
> problems...and I noticed with a warm/hot engine if i unplug the ISV the idle
> increases to about 1200rpm. Plug it back in and the idle returns to 850rpm.
> Isnt that wrong?.  I thought and have seen if you unplug the ISV the idle
> drops to ~500rpm and then plug it in then you get the normal 850rpm.   Can
> anyone verify that?  If so that may mean i have way too much air going into
> the engine at cold start.

Sounds like the ISV might be correcting for excess air getting through
elsewhere.  A metered or unmetered leak - from outside, or, say, past
the ISV/throttle body.

> The duty cycle must be way off if thats the case. When hot should be 25-27% I
> wonder if its higher now.

It starts high and drops, yes, to 27%.  Minimum you can get from it is
25%, as I recall.  I suspect your problems may be elsewhere - as Ben is
fond of chiming in, replace the CIS temp sender on the bottom of the
coolant neck, he has seen a lot of bad ones.  Costs about as much or
less than that meter.  Although, with the meter, you can measure it's
resistance in ice water and boiling water and get a good idea if it
works right.  Bentley has the resistance figures you are looking for.

And thanks for the meter tip, if it holds up and is easy to use it's
bound to be featured in future photo essays...

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/