One of our cars has a bit of a rough idle which disappears at about 1,000 RPM. After eliminating everything else I concluded that this is due to a minor vacuum leak. This was confirmed by the use of a gauge connected to the system, which showed the pressure rising (i.e. losing vacuum) when it should have held steady.
How can I test the vacuum system without actually dismantling its numerous parts and testing each hose, valve and fitting individually? I've considered piping smoke through the system and seeing where it comes out but some of it won't tolerate positive pressure, even low pressure.