Vacuum-leak question...please clarify

[Alex Kowalski (audial@aol.com) (Law Guest Account) <lawguest@wppost.depaul.edu>]

Please excuse my ignorance, could somebody please clarify this for me?

Alexander Mierzwa wrote:

> With the engine idling, remove the oil dipstick.  If the revs drop it's OK,
but if the engine stalls or is about to stall you have a vacuum leak.

I was under the impression that opening the oil-fill cap or removing the
dipstick should <cause> the engine to stall or come very close if there
are <no> vacuum leaks, because opening either of these two orifices
<causes> a vacuum leak which drops the throttle plate suddenly and
makes the engine stall?  Isn't the crankcase being under vacuum what
causes the rear-main-seal whistling?  

I am confused.

Best Wishes,
Alex