As a technician has thoroughly explained on the TME website (go there for specifics) the ECU detects the changed boost rod response and adjusts accordingly. In fact, if you turn it far enough, the ECU will shut off the engine.

Someone recently has opened a thread about a Dawes manual boost controller, but you want to be careful with something like that, too. The ECU won't detect it, bhere are reports of things like bent rods, and other undesireable outcomes with such devices.

The best solution is the most expensive: a new ECU program, such as the one offered by IPD. Recent threads here indicate a high degree of satisfaction (and an occasional check engine light).
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(98 S70 T5SE misc mods, mostly lighting) (92 940GLE)