Air mass meters are fitted to the air intake system, just after the air filter. They measure the amount of air entering the engine. The ECU then uses this information along with data from other sensors to deliver the correct amount of fuel dependent on speed and load of the engine.
Air mass meters are quite delicate and do fail occasionally. Sometimes the engine management light will illuminate and the diagnostics will list the air mass meter as faulty, but not always.
Suitable for the following models:
Land Rover: Discovery, TD5, 1998-2004
Land Rover: Defender, TD5, 1998-2006
Land Rover: Freelander, 2.5 V6, 2001-2006