All I can tell you budha is this (and I know not if it assists you)

Whilst driving home on the motorway my wife reported that the 4.2SC lost power and at the same time she got a Reduced Engine Performance dashboard warning. That fault cleared after the car was switched off and re-started. Main dealer said they later plugged the diagnostic tool into the car and the reason for the reduced engine performance was because the water pump had failed (connected to the supercharger I think/ mechanic said it was a known issue on the SC). They replaced the water pump and associated cabling.

http://www.fullfatrr.com/forum/topic24398-30.html

OK thanks

Is this an SC? If so you may need to check the aux water pump used for intercooler cooling.

No vogue 4.4 petrol

As stated before, Budha, I had this on & off for a year with my last FF. Crucially (!) with the same engine as yours . . .
All sorted with a new MAF sensor - I know you mention you've had this replaced but I'd try another as it sorted my problem completely -

 Where do you go after one of these . . . ?

OK thanks will have to try again

Just spoke to someone who says maybe an air leak so smoke test and software update might do it. Fingers crossed.

a bit of air intake (carb) cleaner through the maf wont do any harm. Over time they can get a build up of fine dirt on them.

I had this very same problem yesterday on my 4.2SC. Admittedly I was being fairly heavy with the right foot at the time on the motorway (late again), but the warning 'Reduced Engine Performance' flashed up on the dash with an audible alarm. From that moment on, the power was indeed reduced. Kept cruising at 70 very happily, but if I went to put my foot down to overtake...nothing happened. Got to where I was going and parked up for around 4 hours...after that (and fingers crossed) it seemed fine.

Will monitor and get the aux water pump checked. Life is what happens while you�re making other plans.

^^

You'll get that on a misfire , the ecu cuts off the fuel to the cylinder/s which have logged as misfired and the reduced performance bongs then disappears , all becomes good again after switching off the engine.

Ah, ok. Thanks.
Is this something I should be overly concerned about? I mean it's obviously not an ideal situation, but should I get it looked at ASAP, or is it one of those things that can probably be monitored for a while? Life is what happens while you�re making other plans.

Could get the codes read, should have stored one.... could be a coil pack breaking down, they tend to go intermittent before finally breaking... that's the usual fault item...  Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
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Had software update and smoke test. No leaks found. Terraclean done........still fault remains but car goes like stink. Getting frustrated now.