cold start problems - continued

[Ti Kan]

I assume you have a 90 with the CIS-E3 injected 130hp NG engine.

The cold running idle boost is provided by the idle stabilizer valve
under ECU control.  The ECU gets the cold engine temp condition from
a thermal sensor (I don't have the Bentley for your model so I
can't ascertain the exact location of it).  In addition, that same
sensor also tells the ECU to run in open loop mode, so that the ECU
will ignore the O2 sensor output until it warms up.  During this time,
the ECU enriches the fuel-air mixture via the differential pressure
regulator on the fuel distributor.  I would suspect that your thermal
sensor is either disconnected, not making good contact, or defective.
Look for it in your Bentley manual and check it.

Once warmed up, the idle speed is regulated by the ECU via the idle
stabilizer valve, based on the idle switch on the throttle body
as well as the RPM signal derived from the ignition.

-Ti
2003 A4 1.8T multitronic
2001 S4 biturbo 6-sp
1984 5000S turbo
1980 4000 2.0 5-sp
--
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Laboratories, Sunnyvale, CA. USA
  ///    ti at amb.org
 //////  http://www.amb.org/ti/
///

Steve Ensch writes:
> I am still diagnosing my cold start problem on my 90.  What controls the
> idle enrichment: as when the A/C is turned on, or during starting a cold
> engine and the idle is automatically raised to 1200 rpm for about two
> minutes or so.  Is it the ISV or a fuel enrichment.  Currently, the engine
> wants to idle at 900 rpm no matter hot or cold, before it used to bump the
> idle up during warm up.  Currently when I depress the pedal with a cold
> engine it shutters or simply stalls or when I depress it even more I hear a
> loud pop from the air box, and the rpm will climb.  More often than not I
> have to restart the car 4 times before it actually will idle without
> stalling.  What controls the idle in this beast?
>