re. Still NF idle problems

[Ben Swann]

Idle and ISV related issues tend to be problematic on the high compression NG/NF with
CIS-EIII.   In theory they should do better than the older engines without as much
computer control, but the ones I dealt with tended to give me fits in sorting them out –
in part since the computer messes with the timing to adjust idle, in addition to the ISV
circuitry. 

That said, it almost sounds like there is something else going wrong and my initial SWAG
is O2 sensor.  A failing o2 sensor can throw things out of whack – usually XS lean
condition, expecially when accelerating from a standstill.  When they start to fail,
often the car will run beautiful and all of a sudden sound like it is throwing a rod.
One indication of impending sensor doom is when the car runs fine on startup, but as
soon as closed loop operation kicks in a minute of so into driving, driveability goes
south.

Other items that can cause similar problem include the temperature sender which give
incorrect signal to ecu on warmup.  Also, the differential pressure regulator – mainly
if it get fouled bay bad gas, but I wouldn’t start by looking at that.

I assume you already verified ISV and related switch, wiring, etc., so it might be some
of the things mentioned above.

HTH,

Ben

[Date: Tue, 30 Oct 2007 21:24:10 +0100
From: "Eyvind E. Spangen" <200q20v at bluezone.no>
Subject: Still NF idle problems
To: <quattro at audifans.com>
Message-ID: <001101c81b32$d486add0$7d940970$@no>
Content-Type: text/plain;	charset="windows-1250"

I'm still having a problem with the idle on my '89 100Q with NF engine.

When cold, it will start right up and jump to around 2000 rpm for 2-3 seconds, then drop
down and stall. (I suspect the high idle is when the cold start valve is powered) I have
to keep some pressure on the gas to keep it alive for the first minute or so. 
When warm, it's usually ok, but sometimes it will idle too low (around 400 rpm),
sometimes it will miss and pull very slow when accelerating too.
If I unplug the ISV, it will idle a bit higher, the normal idle will be too high and the
low idle about correct. Appears OK.

I have removed and checked *everything* except the injector seals. It behaves a lot like
false air. When it idles OK, it will be perfectly fine, and it seems weird if a leak
from the injector seals can appear and disappear randomly..

Any clues?

--
E. Spangen]