vac leak

[dsiegel360]

88'930, Koklen I/C.(BOV removed)..My PLX vac gauge measures 11- 14.5 psi of vac at idle. The vac is measured from the hose connecting the diverter valve and the T behind and below the throttle plate- the line connected to the WUR. I am told that the vac reading should be somewhere between 16 and 20 at idle. ...The timing is set to 25 degrees @ 4000rpm's. I believe that all the hoses have been checked. The manifold nuts have been tightened. I haven't done the time consuming pressure tests and am hoping to not have to. When cruising at 3000rpm's the reading is sometimes 16. Deceleration may bring 19-22. I have tested with Ether and couldn't find leaks. If idle timing is set at TDC, could this lead to decreased vac pressure? Any thoughts or suggestions?