Ditto what norm said. Adjusting the idle stop will do nothing unless your idle speed controller or control system is malfunctioning.

If your manifold vacuum gage reads 400 mm Hg. that would be 15.7 inches Hg. not "psi". The other signal you are measuring is not actual manifold vacuum.

The signal you are measuring at the line to the EZL sounds like actual manifold vacuum, but it doesn't affect timing at idle, which is fixed at 9 BTC.

My engine has a nipple on that manifold with a rubber cap that I remove to attach my vacuum gage. Very convenient.

If you have some kind of operational problem, why don't you just list the symptoms and someone can probably help out.

Duke