Air leaks in FI Spider 2000

[Byas U Nambisan <Byas_U_Nambisan@domain.elided>]

My search continues for the potential cause/s for the idling problem on my Fiat.

I've eliminated the AFM, Aux air reg, cold start valve, temp sensors, and ecu.  
These checked out fine.  I did discover two air leaks:

1. Vacuum advance unit not holding vacuum - a new one is on order.  This is the 
second one that has failed for me.  Is this a common problem?

2. This one I am not sure about, but, the vacuum hose to the carbon canistor    
   does not hold any vacuum either.  How does this work?

     My take is that the fuel vapor from the tank goes to the carbon canistor 
via a valve.  The vapor is adsorbed by the Carbon.  When there is high manifold 
vacuum, the carbon releases the vapor into the manifold.  So far it does not 
seem controversial, but my next guesses may be...

     During high vacuum the valve on the vapor line closes permitting the 
pressure in carbon canistor to drop, and therefore release the vapors.  When 
there is no vacuum (engine is off) the valve opens, allowing vapors to go into 
the carbon canistor (rather than into the atmosphere).

     If this is how it works, the line to the carbon canistor should hold a 
vacuum, and I should check to see if the vapor valve is working or fitted 
correctly.  For now, I've disconnected the line and plugged the port on the 
manifold.  This seems to have improved the idling, although the Vac Adv unit 
leak is still present.

Can anyone validate/refute my theory?  Has anyone checked to see if the line on 
their cars hold vacuum or not?  Would appreciate any inputs.

Still on my list is to check for air leaks at the manifold plenum gasket and at 
the injector seals.

Regards,
Byas