A professional smoke test is your best bet. Sometimes you can find these leaks through visual inspection or strategic spraying of volatile fluids around the engine bay. Plenty of discussion of this topic including a thread on how to build your own smoke machine, you just need to search them out. Cracks in the intake boot between the MAF and TB are pretty common as are cracks in the numerous hoses attached to the intake manifold. A leaking DISA gasket is also relatively common.
Originally Posted by Sean172
How do find a vacuum leak?
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