if you think you are able to hear a vacuum leak there is an easy way to test for that. with motor running spray something flammable like cold start, or intake cleaner around were u suspect vacuum leak is (be sure not to spray to close to were engine actually intakes it air from or it will give you a false positive) if the rpm changes then you know you have an intake leak and were it is comming from. the traditional gas to use is propane but with the vx intake plenoum design it will be very hard to use because it is light than air. i really think before you throw anymore parts at it you need to do some real diagnoises, i also think you should be checking your valve adjustment like i allready said. and if you think it is your fuel pressure regulator then hook up an external guadge and see what you have for pressure, keep in mind that at idle fuel pressure in the line is lower due to low pressure in intake
just my 2 cents hope this helps