David --

The knock sensor is mounted high on your engine block, just under the head gasket seam. It's on the driver's side, midway between cylinders 2 and 3. It's almost under one of the temperature sensors -- about 1-2" back from it ('though the temp sensor is in the aliuminum head, just above the head gasket seam).

The "vacuum set-up" sounds like your constant idle speed valve, sometimes called the CIS motor. It's controlled by the computer and opens slightly if the rpm drops, and closely slightly if the rpm increases. It bypasses a little air around the throttle valve.