Limp mode loss of power just creeps along at about 20mph and will pick up to about 50mph gradually and a few clouds of black smoke now and then

Question edited for clarity.

I think you will find it is called 'Limp Mode'. It is the Engine Control Module finding a fault so serious that is might permanently damage the vehicle. You need to connect it to a Scan Tool and read the codes. The codes tell you the problem and the fix.

Limp mode

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Complete List of OBD Codes (DTC') on Volvo Cars - Erwin ...

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Complete List of 2259 OBD Codes (DTC') on Volvo Cars. Accessing and erasing Codes. The engine control module (ECM) fault memory can only be accessed and ...

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When was it last given a Major service? Black smoke is usually a sign you engine is running 'Rich'. This means the Fuel and Air mixture has too much fuel in it. Are there any warning lights on the dashboard? If it is going into 'Limp Mode' the ECU, (the cars brain), has detected something it thinks is serious. You should get the vehicle plugged into a diagnostic system or an OBD2 scanner for the Error Codes as these are clues to the problem. Try a few different garages as the costs for this service can be very different.
Old Fuel and Air filters can alter the fuel mix. Other areas to check are the EGR valve, fuel injectors and the Catalytic converter.

If you're comfy with manuals then i know few websites that can help you with it. B cause I've got manuals from various websites so I know how each site deals. try https://big-manuals.com/ . Very helpful

Sounds like limp home mode , throttle position pot. ?

Toyota Hilux engine power loss Questions & Answers - Fixya

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Toyota Hilux cars & trucks engine power loss questions and answers. Ask your Toyota engine power loss related question. ... Question about 2006 Hilux 3.0.

go to your land rover dealer seems your engine needs an overall

disconnect the EGR valve and block it off with gasket made from a coca cola can

Yes, I have the same problem, did you find a solution? My corella verso is doing exactly the same.

When were the fuel filters changed.sounds like you have water in the fuel.Drain the tank and try new fuel after changing fuel filter.If it was in limp mode you would not get the revs droping down then smoke then picking up.Limp mode only alows you to do about 40mph.

check the hose on the intercooler and around the turbo, check for split on turbo and the intercooler hose not too soft as they can collaps while driving