I noticed the same thing with my 84' 911, in that the engine tended to
"hunt" while stopped,  particularly when I switched from highway driving to
town driving. So I asked a reputable local Porsche mechanic about it, and he
told me that although it was annoying, it was nothing to worry about.
Explaining that the fuel injected 3.2's are picky when it comes to air fuel
mixture, and that a sudden change in engine operating temperature (i.e.
switching from highway to town driving) would cause enough of a change in
air fuel mixture to cause the "hunting" I was experiencing. I noticed that
if I didn't lug the engine around town by running it at slightly higher
RPM's in town, it doesn't "hunt" nearly as often at stops.

I'm sure one of the true Porsche "wrenches" that contribute to this group
regularly will have a better answer (which I will take MANY notes on!) and
hopefully I may end up with a better fix for my 911 as well. But I just
thought I would share what I experienced, and my results. I hope this helps?

Good Luck!

Lynn
84' 911 Targa

leaks in the intake system are a common issue, especially in the older cars.
Idle "hunt" is a frequent result as the 3.2 DME attempts to compensate for
the unmetered increase in air flow. With lots of rubber components, gaskets,
& hoses, the leaks can be in a number of places downstream from the air flow
sensor.

Finding the leaks can be as simple as visual examination, looking for cracks
or dislodged connections. Then there's the use of a propane torch, unlit,
directing the gas at suspected spots & listening for changes in idle speed.
On my own '84, I found that my intake manifold gaskets had deteriorated to
the point that some of the bolts were only hand-tight. Tightening didn't
help so I changed them all [12].

HTH,