Use a propane torch with the gas turned on, but not lit. As you move the torch tip around the vacuum lines, brake booster, etc., the engine speed will pick up and/or the engine will run smoother when the gas gets sucked in by the leak. It's a lot less messy than liquids to find the vacuum leak. Acetyline works, too.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!