TD5 Going to Low Power

I have an 08 110 with TD5. A few years ago I had an issue with the engine, shortly after setting off, would go in to a total limp mode, i.e. would not respond to the pedal at all. It always Googed me at the most awkward and embarrassing of situations like traffic lights or crossing a busy road. I quickly diagnosed the issue to be extreme cold weather related but, despite many times in the garage with my Landy experts, and many parts changed such a MAF etc, the problem was never resolved. Since then the winter mornings and evenings have seemed a bit warmer and I've had no further trouble until now.
Now my engine seems to be dropping in to a low power mode (50%ish) after about 20 minutes of driving. Its as if I've lost the last 50% of my pedal and the engine wont rev above 3100 rpm. The problem started virtually immediately after I placed the Landy back on the road after being stood unused for over a year. It coincided almost to the day after when my ABS pump developed a sticking valve which made me think it might be being caused by that fault as some sort of a safety feature. I've had a new (second hand) ABS pump fitted which has cured the ABS issue but the engine problem still persists. The engine warning light is on permanently. Also, my placing the Landy back on the road just coincided exactly with the start of the latest heatwave and record high temperatures ever recorded. I've been trawling the Landy Zone now for weeks trying to see if anyone has had the same issue. I've seen many examples of fairly similar problems but nothing matching exactly. I've read about problems with the MAF, the turbo actuator, oil in the ECU plug, fuel tank pumps, the list goes on but none of these show up when I have the engine checked on the lap top and my Landy Expert can seem to put his finger on the problem.
When the engine goes in to low power I've discovered that if I turn the ignition off and straight back on again I get full power restored for a few more miles and the problem seems to reset even though the engine warning does not go off. As a result I've become quite skilled at turning my engine off just before I suspect I might get the problem using stopping at lights or coasting as good opportunities to turn off the engine momentarily (possibly illegal). I've found by doing this I can at least get to work without angering other road users.
Coming to work today I noticed this is probably the coolest commute morning for some 4 or 5 weeks now and, hey ho, my Landy went further than ever without going in to the low power mode. I also noted that the engine temperature gauge was slower to rise and didn't seem to go quite as high, just hanging below the horizontal whereas in the hot weather I'm sure it was just above.
The fact that the engine, when running normally, doesn't feel to be running hot, has loads of power, and is very responsive, tells me that there can't really be anything fundamentally wrong with any engine component but it seems odd that turning the ignition off and on quickly corrects the problem for a short while.
After this morning's commute to work, and particularly since my earlier cold weather issues, I'm now beginning to suspect a temperature issue or maybe a faulty temperature sensor although I fully expect all you experience Landrover owners out there will most probably tell me these issues cannot be caused by a faulty temperature sensor. Therefore, I'm appealing to anyone out there, if you have any idea how I can fix my problem, to please let me know. I love my Landy but sometimes it's hard. Sorry for the long explanation but I thought it important to get it all out there.
Thanks.

If it's definitely a TD5 (no longer made by 2008) then l
would suspect a faulty ECU.

The only way to be sure, is to try another one. If you are in the U.K. try calling this guy and see what he thinks, he supplies and also repairs TD5 ECU's and l can recommend him.

http://www.mastaz.co.uk/

Yes I'm in he UK. The registration plate is 58 so I assumed it was 08 manufacture but might be 07.
I'll check out that web site. Many thanks.

Just to add a little more info about the cold weather problems I was having a few years ago. At start up on a very cold morning the initial idle would be very erratic first running smoothly at about 800 rpm but then dropping to 500 rpm and sounding rough like its missing. In this missing state the the engine would not rev over about 3000 rpm which is a similar issue to what I have now but when the idle recovered back to 800rpm and smooth running again the engine would rev right up no problem. The idle would alternate between the 800 and 500 rpm situation for about 5 minutes until the engine warmed up and then all was ok, except for the total loss of revs in those awkward situations I mentioned in my first post, until the next very cold morning or evening. No Engine warning lights came on and my mechanic could never recreate these faults because each time I booked it in with him, the mornings were not that cold. Ironic.
Although the two issues, then and now, are in many ways quite different, i.e. one was during very cold weather and now, it seems, worse during very hot, the behaviour of the engine has some similarities suggesting a possible common fault like a dodgy injector. I'm hoping this will help spark something off in someone's brain somewhere.

l still think it's your ECU.

Hot or cold weather shouldn't make any difference to how injectors perform as the engine (and injectors) will always run at the same temperature once they're warmed up.

Also
Have you overhauled or replaced the FPR? Although, in the case of a failing component such as that, the symptoms wouldn't normally stay the same for years.

No I don't think the FPR is a component that's been changed whilst I've had the vehicle but after researching what the FPR actually is I see that there is a fuel temperature sensor on it. Since my gut instinct is still telling me this is a temperature related problem, because temperature seems to factor in this so much, I was wondering if the temperature sensor could be faulty and cause these issues?
I'm in discussion now with the person you recommended about the ECU and its seems likely that I was wrong about the engine being a TDI. My Landy is registered in Jan 2009 although it's reg is AV58 so it could well be a 2.5tdci. Not sure if this makes much difference to the diagnosis though.
There's another thing I've been noticing but I think I've been trying to put it out of my mind like self denial. It's the fact that, at initial start up, there does seem to be some hesitancy from the engine for 20 to 30 seconds. Its a bit like a flat spot, but it clears up quickly when I start moving.

lf it's a TD5 your flat spot on startup lasting 30 seconds will be a faulty MAF unit.

But unless it was a very late registration, 2009 will definitely be a tdci, which is a completely different engine.

l've never seen a TD5 with a 2008 or 2009 registration but one may well exist somewhere, maybe ex private use such as an airport where it was never registered.

Also the tdci dashboard is completely different, a quick google of "Defender tdci dash" or "Defender TD5 dash" will soon tell you which one you have.

check theo relays are
tight under
the seat that cured my puma flat spot first thing in the morning
and check egr they cause all sorts of different things as the ecu getsk wrong messages just unplug it and go for a run cant hurt nothing but if its sticking closed you will notice your power back

Been on a couple of well earned and just back to work. Thanks both for all the advice which I'll check out and let you know.

My Dash looks just like this below in its basic layout Image from ebya which I think must be a Land Rover Defender Tdci PUMA new style. I do remember someone mentioning to me the word Puma when I bought it.

I hope this will shed some new light on the situation for someone.

Yep, that's a TDCi "Puma" Defender you've got there.

I'm not familiar with that particular engine.

ok lightning thanks for helping. Hopefully this update will prompt someone else to look at it for me.