yes thor that is a good way to find vacuume leaks. However i would suggest using something like starting fluid so it will evaporate and not leave a residue everywhere. Ceaning my IAA helped when i first start the car but once it gets warmed up it just starts doin it again. Lookin for vacuume leaks is next on my things to do, but im STILL waiting on the rain to stop. This website has some good stuff on curing idle problems. Im kinda working my way down the list.
http://www.z-car.net/
this one addresses idle issues and many other things as well..kinda a "technical library" i guess their calling it...i think last website possibly got its idle info from here
Australian 300ZX Owners Association Technical Library: Content / Category / A-Z Index - Everthing is listed in here