If the plenum is goosed the car can still be driven if you don't mind the rattling. The VIS motors can be repaired, but at around £50 each new, not much outlay. The plenum can be tested with the power valve removed as the end of the arm is exposed, so is there alot of play, or no arm visible? oops! If that is the case then a replacement plenum is required. Not a hard job to do for a competent DIYer. 'How to' available for this.