Volkswagen Repair: Possible vacuum leak?, vacuum leak, vw fox

Question
Well, I can hear it in the motor and see it on the tach. The motor will half-way stall then go back up to idle.

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Followup To
Question -
I have an '87 VW Fox with CIS-E.  When I'm crusing along and come to a stop or otherwise let off the gas, the rpms will go real fast down past the idle point then back up to idle.  Does this mean a possible intake vaccum leak?  All tune-up and fuel stuff in new within the last year.
Answer -
Now ,is this a forsureity (you can hear it in the mottor)or are you going by the tach? See, tachs do faulter as well.  Not a vacuum leak beccause it would continually go up and down and would not idle at a constant rpm.   More like a fuel flow problem, change fuel filter (in a carburated car I would adjust the float in the float bowl so there was more fuel in there.  

Answer
Sounds like your fuel mixture is wrong which could mean a vacuum leak.   Get yourself a spray can of disc brake cleaner and spray it on joints and various vacuum hose connections while the car is idling.  If there is a change in the idle(speed up of dies) you have found the source.  The cleaner is safe to use on rubber parts and also burns.   So never fear there.  Spray it in places that should be tight because of a gasket or clamp on the intake side  eg base of the carb,sides where the linkage  is, intake gaskets etc.