Yup... if the intake gasket is not the issue (sounds like it is the culprit) then grab a vacuum pump and check the actuator, and lines for leaks, and normal operation of the VSV.
Do you have an EDIC motor on this engine? Could be the EDIC is failing or has failed. Can't remember if they are adjustable or not, as it sounds like it is not quite cutting off the fuel all the way.