there is a vacuum line to the sai system. here's a diagram of the vacuum lines:
L and B are the two boots on your intake system that join the plenum to the manifold - this is where the vacuum comes from (there is also a vacuum line for the brake booster that comes direct off the intake manifold, and a vacuum line for the aos on the upstream side of the throttle body).
B feeds the fuel pressure regulator (C).
L feeds a one-way valve (H) then charges the vacuum tank (F).
Vacuum is provided to J/K which is the resonance flapper control (J is an electric valve that, upon signal from the ecu, sends vacuum to K which activates the flapper).
Vacuum is also sent to another electric valve (E) which is tied to the SAI system (D).
there are a couple of 'T' fittings in the system - G and I. you'll note that there is an untapped branch on I - I can't remember where it goes to, or if it is blanked (I have a post on here someplace from when I did remember what it did ...).
so, a vacuum leak in this system can affect fuelling (either through incorrect air readings or improper operation of the resonance flapper) and affect the SAI.