Nodge68 said:

It could be loads of things. You need to go through everything carefully.
Check the vacuum pipes, as those are known to chaff and crack.
Check the boost pipes for leaks at the clips.
Clean out the inlet manifold of the accumulated goop that builds up in there.
Check the air filter is clean.
Check the boost control solenoid is operating correctly.
Get the live data read, looking at the low pressure fuel rail, the high pressure fuel rail, boost pressure and MAF signal.

That'll give you something to start with.

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andyfreelandy said:

The Freelander 1 has a connector behind the centre console for connection of a diagnostic box. The correct box can read fault codes and live data. Live data is the actual values of the engine inputs and outputs whilst running or not!! E.g fuel pressure, revs, manifold pressure etc.. Read up on OBD = on board diagnostics. Gadget to read this info has to be correct one for age and type of car. Land rover need a special one until 2001 for petrol and 2004 for diesel and then a cheaper more basic device can givee some info. More expensive more specific machines are needed for more detailed info.

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