You're assuming wrong.  The 85 used R12, as does mine.  The IS didn't used to work, and was replaced with another used unit.  After see time I determined the problem was a recessed female connector in the IS plug.  Once that was fixed, the IS worked pretty much properly.  I fixed the AC this summer (after over ten years of not being used), and only in the last few days realized I had this high idle issue.  

Karl Wolz
Sent from my electronic umbilicus

On Oct 24, 2012, at 8:19 PM, neil n <musomuso@gmail.com> wrote:

> Was going to ask "what MY?"      ;^)     Figured it was 2.1 engine management.
> 
> Assuming the 1.9 AC compressor is the same as used in the 2.1 and that
> your IS was working ok before......
> 
> Seems to me the ISV is getting more juice than it needs and the valve
> is opening too far or for too long.
> 
> Maybe disconnect the single green/white wire in engine bay, then with
> AC off, try the PS and see how things are affected.
> 
> This is an image of a stock 2.1 engine bay, but AC wire for ISV module
> is shown in upper LH of image: http://tinyurl.com/84py84k
> 
> (I don't have AC)
> 
> Neil.
> 
> 
> 
> On Wed, Oct 24, 2012 at 8:10 PM, Karl Wolz <wolzphoto@q.com> wrote:
>> May be.  My apologies for not mentioning - 2.1L digifant. The AC system is stock '85.
>> 
>> I know the IS should maintain around 850.  It doesn't, but rather, it seems to overcompensate.
>> 
>> Karl Wolz
>> Sent from my electronic umbilicus
>> 
>> On Oct 24, 2012, at 8:02 PM, neil n <musomuso@gmail.com> wrote:
>> 
>>> Isn't the IS system supposed to more or less keep the idle around 900
>>> RPM when the AC load hits it?
>>> 
>>> I don't have AC, but PS turned hard, idle moves a little but the
>>> system keeps it around 900 RPM.
>>> 
>>> I'd have to bust out my Digifant pro manual, but IIRC, isn't there a
>>> current check one can do?
>>> 
>>> Neil.
>>> 
>>> On Wed, Oct 24, 2012 at 7:05 PM, Karl Wolz <wolzphoto@q.com> wrote:
>>>> As my AC cycles off and on, my idle changes from 900 or so to around 1800rpm.  Seems to me the IS is trying a bit too hard.  Suggestions?
>>>> 
>>>> I have a spare, but pulling the tail light is a lot of work. ;-).
>>>> 
>>>> Karl Wolz
>>>> Sent from my electronic umbilicus
>>> 
>>> 
>>> 
>>> --
>>> Neil n
>>> 
>>> 65 kb image Myford Ready For Assembly  http://tinyurl.com/64sx4rp
>>> 
>>> '88 Slate Blue Westy to be named.
>>> 
>>> '81 VanaJetta 2.0 "Jaco"  http://tubaneil.googlepages.com/
>>> 
>>> Vanagon VAG Gas I4/VR Swap Google Group:
>>> 
>>> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines
> 
> 
> 
> -- 
> Neil n
> 
> 65 kb image Myford Ready For Assembly  http://tinyurl.com/64sx4rp
> 
> '88 Slate Blue Westy to be named.
> 
> '81 VanaJetta 2.0 "Jaco"  http://tubaneil.googlepages.com/
> 
> Vanagon VAG Gas I4/VR Swap Google Group:
> 
> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines