Vacuum leak?

Having trouble when switching from vent to defrost
to floor. Any switching from one to another only
happens when I let off the pedal then I hear the
clunk when the doors move with a surge of
vacuum. It also idles rough but fine when driving.
Sometimes the engine surges after starting when
engine is still hot from normal driving. Once going
again it stops. Have replaced idle control sensor
with no change in symptoms. Gas vapor purge
system is all good.  Brake booster and vacuum line
good. Can't find a vacuum accumulator or any
other vacuum lines to inspect for damage. Any
help will appreciated.