I was checking my idle vacuum today (which I haven't done before) and it was low- only 12 in. Hg. The engine is a B23E with the K cam. Ignition timing was correct 5 degrees+-2BTDC, compression is 175 all across (I should say 'was', as this hasn't been checked in a couple of years). No obvious vacuum leaks, no manifold leaks. Have not checked injectors (K-jet) yet.
I did some searching on the 'net and found that incorrect valve timing can produce exactly the same results that I have (12 in.Hg with a small vibration of the gauge needle). If the timing belt is off one tooth it produces very poor driveability, does it not? The car drives fine. No problem accelerating. It is tired- 302,000km (gives a little puff of blue if I shift out of 1st over 5000rpm) and was not well taken care before I got it. But it is good tune now: good plugs, wires, cap and rotor.
I have heard that lopey cams (ie. the 'k') produce poor vacuum at idle. Is this accurate? If the warm weather holds I will take a more in depth look.

As always, any insights are appreciated.