Pre heat light

Hi looking for advice I've got a man tge 180 and the pre heat light keeps coming on. We've changed the glow plugs, both turbos and the 4 sensors. Thought we had cracked it drove near 100 mile and pre heat light comes back on and goes into limp mode, coming up with error code PO2990 turbo under boost. But if you switch of ignition it clears it for another wee while. Any assistance with this would be much appreciated as am tearing my hair out

imm6140 said:

We've changed the glow plugs, both turbos and the 4 sensors.

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What was the reason for the parts replacements? New OEM turbos? Did the turbos come with new actuators?

imm6140 said:

the 4 sensors.

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What sensors exactly?

imm6140 said:

error code PO2990 turbo under boost

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Anything more? The ECU made a snapshot (called freeze frame data) at the moment of fault - can you access the data?

Air leaks or vacuum leaks ruled out?

According to the dealer the turbos were faulty i would hope they came with new actuators the cost of them! , not sure on sensors 3 were changed with turbos the other was an original which was supposed to have cured it but still the same. That's the only code it was showing PO2990.
What they are saying now is it "could" be valve in the exhaust at MORE COST! any suggestions would be much appreciated.
Thanks

Sorry, but next to impossible to say anything definite. Would need extract diagnostic data from engine with a proper diagnostics tool to understand what's possibly wrong.