the vacuum pipe goes from the turbo actuator(what you pulled it off)back to the boost solenoid(position could be close to intercooler and damged area)
so pulling the vac pipe off the vnt actuator resets the limp mode ?
you need to confirm if your car is overboosting or under boosting really.
also you want to check the condition of the vnt vanes in the turbo by starting and stopping car and watching vnt actuator and arm move
similar to this , but will suck in on starting car and come back out on stopping the car. where im actuating this with separate vac(syringe)
Vnt actuator 100ml syringe operating it - YouTube
also worth checking when at idle it is pulled in all the way to the stop screw on the turbo body, if not maybe a solenoid issue or a vac leak from hoses or sticky vanes.
if you do the same with engine running and pull the vac pipe off, does actuator go out approx. 10mm, when you refit the pipe does it pull back in approx. 10mm either direction you want nice smooth movement no jerkiness and travel in around a second or two.
a local garage should have a vac gauge they may lend you to check , just pull pipe off turbo and stick on vac gauge , should be around -600mbar vac at idle.
Vac at actuator pipe - YouTube
id suggest a cheap obd lead and free software like fes now multiscan to save some guesswork.