Help: O2 sensor & idle

[bgsterling at bluebottle.com (Brad Sterling)]

<snip Cory> 
I figured the o2 sensor must be on the way out, 

<snippage>

In the process I have disconnected the cold start injector and the aux air
valve.  

<snippage>

The thing that is strange is when I start it up and the engine is cold, the
idle jumps up to 1800.  Once it gets to normal operating temp, the idle
drops down to a nice 1000.  
<end snip>

Okay, since no one else spoke up, I'll throw out my .02.  This is coming
from someone with a mostly stock Mk2 16v, so take it for what it's worth
when applying it to a Mk1 Turbo.  This is my thought process:

*  The o2 sensor, which is on its way out, is creating a fuel rich situation
(limp home mode?)
*  When you start the car, the engine bay is filled with cool dense air
*  Cool dense air + rich mixture = mixture closer to stoichiometric and
higher idle
*  As the engine bay warms up, the air gets less dense
*  Warmer air + the same amount of fuel = mixture further from
stoichiometric and lower idle

I'll bet that once you've got a working o2 sensor adjusting the fuel
delivery properly, your idle will behave more predictably, given that the
cold start pieces have been yanked (e.g. low when cold and good when warm).

-Brad
'86 Scirocco 16v