I can't "pinpoint" the source of your vacuum leak, as you have a network of vacuum hoses to check.
The first places to check though is the "bellows" looking unit next to the air mass sensor...look for any signs of deterioration (cracks, etc.). Replace if necessary.
The large majority of leaks would probably reside near the intake area. Inspect the condition of the hose fittings and the smaller vacuum hoses.
Some here will run the car and spray starter fluid near these areas (sounds dangerous though). If the engine idle suddenly increases when you spray at a particular area, then you have found the source of the leak...this is the stage where I am currently at right now.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car