Low Vacuum???

OK, I thought I had a vacuum leak, probably still do but I can't seem to find it.

I'm reading 10-12in at idle (900rpm). I've disconnected everything, plugged everything, pressurized everything, squirted propane all over the engine bay, and I can't find any friggin' leaks.

I haven't messed with the idle control solenoids on the right side of the intake. Could they cause a vac leak?

Is there any reason that I shouldn't be running 18-20in of vac? Too much valve overlap? Low compression? I can't figure it out...

Maybe the intake manifold has a leak in the gasket somewhere? I would think that I would have found it with the propane...

Thanks in advance for any help...

Gabe