If you've got a propane torch, introduce propane slowly around suspect fittings and connections while the engine is running and wait for the engine's idle to change.
Carb cleaner and/or starter fluid works too, just don't spray around plug wires or ignition coils. And if you do...well, your eyebrows do grow back eventually.
The number one suspect area is somewhere in the PCV tube assembly coming off the passenger's side valve cover to the intake manifold.
!@#$ the language filter.