Sixto is exactly correct. You need an external vacuum source if you want to measure readings with the engine off, and you really don't want to do this with the engine running, unless you don't mind having your hands and face right on top of a motor spinning to 5000rpm (personally, I don't like that).

I use a venturi-type vacuum "pump", about $15 or so from Harbor Freight, but this requires a compressed air source to power it. Otherwise, a second vehicle (gas or diesel) will work for a vacuum source, just get a 10-foot length of vac hose from McParts, and hook it up to the other car to get a steady vacuum source.


Also - the FSM specs in mbar are kind of a pain to decipher. If you provide 15" (or more) of vacuum into the inlet of the VCV (located on the side of the IP), the output should measure 12-15" (approx) with the throttle at idle position, and this should smoothly decrease to zero vacuum at WOT. At least, that's what I measure on my cars, and mine all shift normally...