high idle

[Mark Zvolanek <mzvolane@sydney.ipex.com.au>]

Gday fellow Audi fans
Since I replaced the idle micro switch in my '91 90 the idle has heen   
doing OK.
Except ...
As the engine warms up, around 10 to 15 minutes from initial start, the   
revs increase from 800 to 1000 RPM. The increase happens in stages not   
all at once. Would anyone know what might be causing that.
I read in recent posting low voltage can cause high revs, how is that?
What should be the correct voltage supplied to battery from alternator,   
and how much should it drop when for example lights are switched on etc.
My car is a manual, FWD.
Any help will be welcome.

/\/\ark Z\/0LANEK