A leaking vaccum system, can actually cause the engine to run poorly.(any engine that is... not just murenas, and their fancy popup headlignts
)
This issue should be addressed, as a leaking vaccumsystem can be a place for the engine to suck in "false" air.. (air that hasnt been mixed with fuel on carburetted engines, or air that hasnt been mesured by the Airflow meter on injection engines).
I have no experience reguarding the 1.6.
But the general oppinion on the forums i've been to is, that tuning the 1.6 is a waste of both time and money. It is.. after all, an ancient design that allready was pretty much obsolete before they even put it in the Murena.
So to me the only real way to more power is an engine swap.