Idle screw on NG engine

[David.Ullrich at ferguson.com]

So, any suggestions on where to start? If I close the screw all the way the engine idles so low that the oil pressure light comes on and the idle is a bit rough. Also, at times my idle bounces between 800 and 1600 when the car is warm. If I shut it off and restart it will idle perfectly for a while. The problem is VERY intermittent, it may go for days at a time idling perfectly then have problems for a day or two. I have already "cleaned" the ISV with lots of throttle body cleaner. It's nearly spotless. When 12v is applied, it seems to open and close fine (fast)... Any help on where to start would be appreciated.

TIA!

Dave

1987.5 Audi Coupe GT "Special Build" 2.3 - Anthracite Black
1998 VW Passat GLS 1.8T - For Sale CHEAP


-----Original Message-----
From: Huw Powell [mailto:human747 at attbi.com]
Sent: Wednesday, April 10, 2002 3:49 PM
To: DGraber460 at aol.com
Cc: David Ullrich - 0018 HQ; quattro at audifans.com
Subject: Re: Idle screw on NG engine


"In order to get my idle where it belongs, I've had to play with the
idle screw on my Coupe GT (2.3 NG). But somebody told
me that if the engine is tuned properly and there are no vacuum leaks
that the screw should be closed all the way and the
ECU will control the idle. Can anyone confirm whether this is true?"

> Air _must_ pass into the engine at idle. If the throttle plate is adjusted
> properly, it should be nearly closed allowing the idle "bypass" screw to
> "fine tune" the amount of air for idle. The ECU can control the amount of
> fuel and timing advance, not air.

The ECU controls the air via the idle stabiliser valve.  The 87.5 Coupe
GT NG setup still has a "legacy" idle screw - which is not even present
on the later NG's.

As the throttle plates shut, the idle switch is activated, and the ECU
takes over, running the ISV and fine tuning its duty cycle by reading
RPM.  (and also setting the timing to 12 degrees BTDC - just barely off
idle, the timing shoots up to about 45 degrees!)

--
Huw Powell

http://www.humanspeakers.com/

http://www.humanthoughts.org/