If the engine light is on or the glow plug light has been flashing then I'd say getting the codes read would be the best options as there are many faults which could trigger loack of power or put the engine in limp home mode.

Simple checks would be to check all the pressure pipework between the turbo and engine for leaky joints or splits/holes in the pipes themselves. These can be hard to see if they only open up under pressure but oil seepage / spatter might reveal the location of any leaks. The rubber bellows pipes attached to the intercooler also tend to wear where the metal spirals sit in the base of the corrugations wo worth checking those for any signs of leakage, as well as checking all jubilee clips are tight.

Also check the small-bore rubber vacuum pipes on top of the engine are all connected and in good condition. A leak here can result in loss of power. A garage worked on my car once and left the small pipe disconnected from a black plastic box close to the firewall and the car lost most of its power. Turned out to be the MAP sensor.

Finally, check the variable vane actuator arm attached to the turbo is free to move and does not stick in position. You need to reach down past the RHS of the engine to reach the turbo and push the arm back and forth to che if it is free to move. Sticky turbo vanes can result in overboost which causes the engine to drop into 'limp home' mode. Cleaning the turbo can stop this.

I'd guess it was the vacuum attached to the variable vane actuator.

No vane movement = little or no boost as the vanes will 'fail safe' in the bypass position, directing most of the exhaust gases away from the turbine.

Good cheap fix!