If the idle increased when you disconnected the vacuum gauge, then it's slightly rich, and thus adding any fuel enrichment (ie: propane or carb cleaner) won't raise the idle.
What makes you think you have a blown head gasket, and if you do, why are you driving it or attempting any other tuning? A blown head gasket is a serious problem and needs to be taken care of before anything else. Any tuning can't be properly done with a bad head gasket either, and besides, you will be replacing all of the intake gaskets anyway when you replace the head gasket. You need to find out if you have a blown head gasket. Check your compression and use your vacuum gauge (your vacuum gauge should fluctuate as you increase the idle speed with a blown head gasket).
Take care
~Chris
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Retired Moderator
MustangNet
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JimPorterRacing
RACECAR spelled backwards is RACECAR
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