Like most have said, it's normal for it to sit at 0 (atmospheric) when the engine is off, and for it to go negative when idle (the motion of the engine literally sucks air into it).
However, if the amount it goes down has changed and you haven't done changed anything (pod filter, boost controller etc), then you might have a leak. Does it still make the same maximum boost? (stock on the 34 is just over 3/4, or half way between 0 - 1) Does it hold that boost if you hold your foot down?