I believe there's only one source for vacuum, and that's the intake. Remove the engine cover and trace all the lines, running off the intake. Besides the sensor(s) and
brake booster, there aren't many items that rely on vacuum anymore. Once you determine what's what, you can begin selectively isolating circuits, with exception to the
brake booster of course, as this is a safety item. If you're missing while idling, or can still generate the miss by revving at a standstill, you could even isolate that circuit.