sounds to me like you have a vacuum/boost leak. i know you said there are no blatant leaks, but i am a little skeptical. (don't hurt the messenger
. )
i had similar problems. turned out that i had SEVERAL loose hose connections and a split hose under the intake manifold.
also, how old is the intake boot? sometimes they have cracks/splits that are VERY hard to find. check also the rubber connectors on the hard pipes/intercooler.
also, have you checked your fuel pressure/flow at the fuel rail?
one last thing: could be your TPS or AFM.