I just bought a 90 tt auto its japan specs, has a stock boost gauge, when i'm idling it sits around -5 and when i'm full acceleration it gets up to around +4. Ive been doing some reading and from what i can tell it should be in the +9's. some sites say detonation sensor some say boost leak. can someone tell me the best way to troubleshoot this problem if there is one? also there is no check engine light on.