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Both our 2.3L LH-Jet cars show 19-20 inches at idle, the K-Jet a little less. Idle vacuum is highly dependent on valve timing, but I would expect your 960 to be a solid 20in. Sounds like it may have a leak or some adjustment is off.
I too have used a vacuum gauge to watch cruise control action, and even on our 4-cyls it does not swing wildly on level highways, it increments up and down in very small amounts. Are you saying yours shows the throttle is going between nearly closed and one-third open on a level road? Something's wrong.
But it is interesting to see how the cruise control works - in discrete steps, not a smooth and gradual movement of the throttle.
You will see no 'ram air' effect (positive intake pressure) at any speed you can realistically maintain on a highway. By the time the airflow gets through the filter, the AMM, the throttle plate, while following the several bends in the intake ducting, the miniscule amount of speed-generated pressure is gone. Actually, you would need a gauge that measures inches of water column (not inches of Mercury or psi) to even see the "pressure" at the front edge of the grille at, say, 70 MPH.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar 77 MGB, and numerous old motorcycles)
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