Waste Gate Actuator
This is the wastegate actuator...
It bolts to the turbo housing via three bolts (position indicated by the green arrows). The capsule (yellow arrow) converts pressure/vacuum to linear motion in the actuator rod (red arrow) to turn the wastegate shaft (purple arrow) thereby controlling the amount of exhaust gasses by-passing the turbo and ultimately controlling the level of boost.
The wastegate often sticks and needs releasing.