Originally Posted by the original
A certain well known tuning garage told me
that one of the first checks they do on a car that comes in is check the idle vacuum with an accurate, large liquid filled gauge
on a standard car it should be x psi (can't remember exactly but something like 10 or 11?)
and if it's not that high (i.e. less vacuum)
then it's an indication of incorrect cam timing, inlet leak or some other problem....
Why on earth are there negative readings on a boost guage in the first place?
Boost gauges indicate "gauge" pressure, ie relative to atmosphere, hence a vacuum is indicated as negative gauge pressure.