Vacuum Leak Detection

[Dave Conner <conner@cfm.ohio-state.edu>]

Who said vacuum leaks can be detected by wafting propane/butane around the
engine and hoses until the engine revs higher...indicating the gas has been
sucked in at the vacuum leak?

I believe my "new" 91 200q has vacuum leak troubles.  So I tried the
propane trick and got nowhere.  
The engine will run with the oil filler cap removed so I even directed the
propane into the oil filler hole and the engine rpm did not change.  I
spent ten minutes directing propane at every suspect hose with no vacuum
leak detected.  

Am I doing something wrong?
Are there other tricks I should I, or do I just need to inspect/replace
every suspect item one by one?

Dave Conner
Columbus, OH