Take a rag, put some throttlebody cleaner on it and open up the butterfly valve. Run the wet part of the rag over the edges of the butterfly valve (the thin part). Then using some of the throttlebody cleaner, also spray at the point where the shaft for the butterfly valve enters the air stream. Any gum where the shaft rotates or on the edge of the butterfly valve can cause this.
Once you have done the above, reset the computer and see what you have then. Obviously you moved something to change the "problem". So, you are on the right track.
Chris "Thermo" Coleman and Jackie, the 12 XJ