Sounds as if you either missed a vacuum hose connection, or possibly the intake gasket did not properly seal. I would use a spray can of something that would not damage your paint (WD-40 or equivilent) and spray around the gasket mating area, etc., while the engine is idling to see if you can locate the vacuum leak. Also, your ignition timing may be "off", but I assumed you have already checked your base timing, etc.. You can also hook up a vacuum gauge to see what kind of vacuum you pull at idle, but these numbers can vary a lot, depending on what your running for cam, etc.. Do all your spark plugs look the same ? This is just a starting point, but these are a couple of the obvious / possible issues. Not trying to offend, but I don't know your level of mechanical ability - so if you've already been there - just ignore me.