Thank very much for this very useful information. I will re-check what I stated about the actuator position over the weekend. I don't know where the boost was measured.

Thanks again for the advice. See my reply to the other contributor above.

Yes. This was shown on the invoice from the Volvo service last year. Thank you for the suggestion. Much appreciated.

Yes, it's twin turbo. It comes as a heavy, chunky unit. Made by Borgwarner. Both were replaced.

Thank for this. Very kind. I will re-check the pipes, more for my peace of mind than in expectation of finding a fault. These solenoid control valves are a bit more complicated than they used to be; the ECU supplies a varies signal to them so that they can vary the vacuum, rather than it just being present or not. One of the first things I did was to swap the two turbo control valves over to see if one was faulty. There was no difference. Because they are relatively affordable I bought a new one (like your link) just in case both were broken. No difference, of course.

I now have a spare turbo actuator, MAP sensor, MAF sensor, Exhaust pressure pipe and sensor and a whopping great BorgWarner twin turbo unit whose replacement cost me €2100 from Rotterdam excluding the ridiculous delivery charge.

What I don't have is a car that works.

Thank again. I'll re-check the pipes as you advise.

Also, I was wrong about the wastegate being open at idle. What seems to happen is a quick open-then-close routine when the car is first started. Thanks to Galilieo and others for correcting me.

Dear Focussed. Thanks very much for the further help with this. I will certainly contact this chap and let you know how I get on. I've had a quick look at the link you sent and there doesn't seem to be much that he doesn't do!

I've made no progress since my original posting, except to say that very occasionally there IS a surge of boost, or power when I clear the error using my cheap OBD device. This is so rare that the car feels like a totally different vehicle for a few moments before power is lost, the gearbox changes down and the revs increase. The "boost" is not experienced every time I clear the error, just occasionally.

I'm now wondering about the possibility of there being a fault with the electronic throttle body, although there are no errors relating to this. It is about the only part that hasn't been replaced.

Thanks again.

Thanks for this. From the outset everything pointed to such a leak. The car has now had smoke tests at three separate garages, including Volvo and with nothing to show for this. I'm sure you'll understand my frustration. Is there anything you can suggest that I do?

How would a smoke test be useful on an induction system, unless there's a camera inside the inlet manifold?

A smoke machine produces smoke / vapour under pressure and introduced into the air inlet tract . Any air leaks will be identified by smoke escaping from any pipes, hoses or joints .

Thanks for that explanation.

Specifically this is for " elekie&a/c doctor"

While I understand what you say about the throttle body in a diesel engine, surely if there was a fault with it, such as it being kept closed or nearly closed because of damage to the motors or gears, this would affect performance? This could possibly starve the inlet of air as I understand it. I certainly claim no expertise in this matter, but admit my ignorance. When I removed the inlet manifold for cleaning (see my original, long post) I could see that the throttle body was a chunky piece of kit with a valve in it with a diameter of about 10cm. The throttle body's mechanism is closed with rivets rather than bolts. I would expect any malfunction of this unit to throw specific errors but I imagine these could be masked by malfunctions. I'm reluctant to remove the throttle body because a) it's a real bore and involves removing the car's intake manifold and b) your suggestion is that it is most unlikely to be the cause of the fault.

Readers of this thread will understand that my head is frequently under the bonnet of the car while I wonder what on earth is the cause of this fault. It's not a minor problem; the car is pretty much undriveable and when I recently had to use an autoroute for a medical appointment, on an uphill section I crawled along at about 70kmh with the hazard lights on.

I would very gladly pay anyone who can resolve this problem many hundreds of euros! Note how much it has already cost me and to no avail.

I disconnected the throttle body and started the car. ODB showed a P0122 throttle position fault as expected but there was no check engine light. The usual P2262 "Turbocharger boost pressure not detected" had been cleared.

As usual, for the first 200 metres or so on the flat, the car drove as it should. Then, again as usual, power was noticeably lost and the car wanted to rev but had little or no torque. Of course, the P2262 error was again shown on OBD.

Thanks for doubting my theory about the throttle body. You were right.

A reminder that three smoke tests at three different garages have failed to show any leaks.

Volvo won't see the car for five weeks, not that they have done anything at all except smoke test change working parts, and say "Yes, Sir. You're correct. Your car doesn't work".

Thanks Gordon Bennet. I did remove the inlet manifold myself and gave it a clean. This process is hidden in the rather long original description above. I did this because Volvo wanted a ridiculous amount of cash to do it and said that it was the "next step" in the process after they'd replaced the EGR valve and EGR cooler body. The inlet manifold wasn't as dirty as I's wanted it to be, if you get my drift. The swirl flaps were fine. The throttle body and butterfly valve were very clean indeed.