Overboost and Underboost Subaru common causes:

How to test your actuator spring rating:

You will need a boost gauge for this unless you have an electronic boost controller. It should have an on screen boost display. All you need to do on the standard boost control system is remove the boost control pipes from the turbo outlet nipple and the nipple on the actuator and fit a short piece of pipe direct from the turbo outlet nipple to the actuator. This allows an uninterrupted flow of air to the actuator and will limit the boost roughly to whatever your wastegate spring rating is, normally 0.5 BAR on standard setups.

On an electronic boost controller all you need to do is follow the instructions on how to switch your boost control off and this will have the same effect.

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