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					Originally Posted by Texasdoc  Yes, manifold vacuum.  Guess one of these days I'm gonna have to pull the intake. | 
	
 I would try shifting that manifold vac source to a 'drier' area of the intake manifold, I think that when you switch the engine off the vac advance unit which has 'high' manifold vac at idle pulls a bit of rich idle fuel mix back in as it returns to a no advance position simply because the current vac source is close to the idle fuel slot.