On the Mk4 Ibiza it's a single combined box - on top of the driver's side suspension turret - that controls all the vacuum supplies (eg boost control, EGR control, ASV control, etc etc).Its one of the valves on the back of the bay, the vac line from the actuator on the turbo goes to it, The valve controls the actuator which in turn controls the vanes in the turbo, this is what effects the boost.
Think they are about £25 from TPS.
hey man, i have endless problems with the turbo! my car is current @ RS tuning in leeds and they are sorting it out for me! i think the bar that controls boost is set wrong meaning that the turbo is boosting all over the place!
Rs tuning are sending the turbo off to CR turbo's where i had the hybrid from to set it again! i have had endless troubles! i replaced all the vacuum pipes, the main unit and it turned out to b the turbo all along!
aint had the car running properly since begining of december! will let you know the outcome.