How would you know if you have a vacuum leak?

first symptom of a vacuum leak would be a shaky idle also a trained ear will listen for a hiss around a vacuum hose also the engine miss usually goes away as engine rpm is increased.find the cylinder that does not changethe way the car runs by pulling spark plug wires off one atr a time with insulated ignition pliers if you have seven cylinders that are strong and one that barley changes idle when you pull spark to that cylinder chances are there is a vacuum lek to the weak cylinder.follow any vacuum hose that lead to the wek cylinder spray carb cleaner on intake manifold gasketr while engine running. if engine smoothes out while spraying gaskets,air is probally entering causing that cylinders fuel ratio to be lean. also egr valves are known to cause intrernal vacuum leaks. a good tech should finbd it in 15 minutes