A well working MAF sensor on the TD5 engine is a must. Ideally you should be getting a reading of 55-60gr/hr at idle, slightly more in colder weather when the engine is cold – anything significantly outside of this indicates a fault and the TD5 MAF sensor should be replaced.
You can check your Mass Air Flow Sensor using a multimeter as shown in this video : https://www.youtube.com/watch?v=JzrP1saTm9A