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ISV (Idle Stabalization Valve) question

My 1988 Audi Quattro 90 idle sometimes "sticks" at around 2k rpm.  It usually
happens when I am coming to a stop and the rpm drops from around 3.5k. Very
rarely the idle shoots up from 1k to 2k and sticks around there for a few
Some of you suggested that this could be related to the ISV.  So now in order
to test whether this is an ISV problem I sprayed it with the Carb Cleaner
but no gunk came out.  And after examining it seems like that the
ISV is pretty much sealed.  
However, I did notice that there is very noticable clicking noise that comes
from the ISV.  I don't know if this is normal or a sign of a bad ISV.
For now I am thinking of disconnecting the ISV and running the car for a day
to see whether the idle stickiness problem reappears.  But I don't
know if this is a good idea.  Any cons on running the car with the ISV disconnected?  And any other simple tests I could perform to make sure that the 
ISV is really at fault here before I dish out almost $200 for a new unit?

BTW, the car has 127k miles on it.