Yeah simply put, you have a little too much cam in there for a smooth idle. Intake and exhaust valves are open at the same time with the overlap which gives a rough idle and a low signal on the vacuum reading.
Stock grind camshafts idle great, just like the 340 grind camshaft that comes stock with the 360 4 bbl. engines. Good idle and good vacuum pull at idle.
So here is the stock 360 camshaft grind>
Lift: 430/444
Duration: 268/276
This grind is probably a little closer to what you have plus or minus:
268 degrees - intake
284 degrees - exhaust
46 degrees of overlap
.450" lift intake
.455" lift exhaust
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