How bad are we talking, in terms of fuel usage?
I'm not impressed with the amount mine uses, but it's a hell of a lot better than my old R34 Skyline or Forester.
The intake gets clogged up by blow-by from the pcv. I've stopped this by making an allow intake, that doesn't let the cam-cover go back into the intake, i'll be putting a catch can in soon.
It's about an hour job to clean the intake, taking off the airbox, intake pipe, throttle body, top intake plenum and bottom intake runners. Clean out with degreaser, or petrol like I had to use, it was that baked on.
Then after you've done that, it's reccomended to use upper engine cleaner, like Subaru guys use.
Oh, and if you do this, you'll need to do the throttle learning procedure, which can be found on google or skylines australia.