Hello my friends car won't go over 70mph and when I ran a diagnostic test the error code p0234 came up. Any ideas how I can fix this? I'm looking for a way to fix it where at the X431 PAD now

It's strange that these people are not really giving you a helpful answer. Perhaps they don't really know anything about this issue.
The reason for a turbo over boost is that the turbos on these cars have a variable vane geometry. The static vanes in the turbo housing move to direct more or less exhaust pressure onto the turbine. That means that at low revs the small volume of exhaust can give good boost but at higher revs the vanes point away from the turbine so that boost is reduced and economy is better. This is controlled by an actuator and the ECU monitors boost pressure vane position and revs to keep everything working right. The problem here is that the carbon buildup in the turbo is making the vanes stick. As you accelerate hard the vanes should go from high boost state to lower boost as you decrease the throttle during a gear change. If the MB STAR C3 stick the boost stays high and the ECU puts the car in limp mode.