Ok' if your vacuum/boost gauge isnt reading eratic then its not an air leak, before i sorted mine out the vacuum gauge was a big give away, was very eratic when the car wasnt idling well (my gauge seems very sensitive however), if i were you, temporarily (or permenantly) disconnect the long hard breather pipe running from the oil control filter to the metering head, this elimiates the whole breather system from interfering with air leaks, any air leak anywhere on the engine with it connected will affect it (loads of possibilities for air leaks).

Its also worth checking the fuel system ir retaining its pressure, do you know how to do this?