Stalling under pressure

[Leonard_S._Ferrara@njmug.org (Leonard S. Ferrara)]

I do not wish to upset the Audi gods, but my frustration level is getting
there.
Car (87 CSTQ5) runs like a top and smooth as silk until I put the A/C on.
Then the idle begins to disintegrate and eventually in the heat, the car will
stall when braking to a stop.
I have over the past two months changed the:
   Idle stablizer 
   Spark plus and wires
   Rotor and cap
and  adjusted the idle mixture, all to no avail.

I suspect some type of vacuum leak(when I pull out the oil dip stick while
the idle is smooth it does get rough but not enough to stall)  BUT which hose
might it be? Does anyone have a good way to test?  Car has 93,000- things do
dry out with age.
Thanks guys. I know someone out there will say "Been there, done that"
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