Yes indeed vac servo type. I do beleive it's under all the other ecu's in the engine bay ecu box (or it was in mine, passenger side front wing not behind the glovebox) It's a silver box, about the size of a cigarette packet. I am informed its a bit of a faff because all the other stuff is on top so many ecu's would have to be very carefully disturbed/lifted aside to get at the little blighter but thats what trained professionals are for

I worked on the assumption that it would be a "shared" item over the models which is why I went looking for repair/problem for non A8 specific cruise problem. And I can happily report it fixed mine up a treat. It works first time everytime.
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PF late '97 D2 2.8 Aluminium Silver. Solar roof, Full Heated Leather, Double Glazing, 17" wheels, Sports Steering Wheel, Cruise, Blinds, Bose sound.
Fiat Tipo diseasel econobox with all the buttons and none of the soul that now does all the heavy lifting.
Ford Capri Laser: noisy, slow, thirsty, bouncy, no buttons but it always sounds like it’s REALLY trying and I can’t help but chuckle when it parps and boings along. And people of a certain age stare at it with a wistful look in their eyes that clearly says…I had one of them. And I sold it because of the kids