We quite often see diesels in the workshop with a very common complaint of lack of power or some people describe it as the kick down not working. Do some basic checks firstly like oil levels, fuses etc. Listen for any escaping air under pressure when you are driving at full load. If this is the case you will probably have a boost pressure leak from somewhere. The common areas are: Intercooler, rubber boost pipes and the inlet manifold itself. If you suspect a boost leak then listen at the front of the engine and see if you can hear where it is coming from while a friend gives the engine some RPM. The next step is to get it plugged into a Star and get the codes read. This is the most important thing to do before buying ANY parts. So many people read the forums and assume there car has the same problem as what they have read and replace the same parts and wonder why it hasn't fixed it. Get it plugged in. It will save you ££ in the long run I promise you. The most common item to fail and nearly always brings up a code is the infamous Air Mass Sensor or MAF (mass air flow). It is always worth doing a manual check with the live data just to be sure that is the cause. A common fault code that comes up is a fault with the boost pressure sensor. It will say either under boosting (lack of turbo pressure) or over boosting (too much turbo pressure). So many people will replace this sensor for this fault when the sensor will be working perfectly. Checking the sensor values with a Star helps determine this. Under boost: Check boost pipes for leakage. Over boost: has it been mapped badly? Is the turbo actuator or vanes sticking? We see quite a few inlet port shut off motors failing too. The V6 diesel, 220CDI and the 270CDI all suffer. This will give you lack of power when they fail and an engine light will come on in the case of a V6 CDI. A check on a Star will bring up codes for this. I hope this helps.