Did you check that the butterfly itself hasn't seized ... I did writew a reply about this ... I had a 1995 Mistral that had the butterfly seize wide open ... if the vacuum actuator had been blocked, then there is the possibility that the butterfly has seized in the closed position.
Take the heatshield off the top of the butterfly, disconnect the adjustable rod by taking the circlip off the butterfly end ... the butterfly should then move quite freely ... if it does not , soak it with WD40 and move it back and forth from the open to close position and back until it is free with no resistance, then connect it all back together. If the butterfly is seized, the ajustable rod obviously won't move. I had to tap the butterfly on mine with a panel pin hammer to start easing it.
I did write a reply to you previous to this one ... check for it, as there is more information on that reply.
Matt.