Rover 75 cdt low torque

Could be -

Blocked or collapsed air filter. Dirty fuel filter. Collapsed turbocharger pipes Mass air sensor fault.

The first two are a good starting point, a blown turbo you would know about.

PDH

Sounds like mass airflow sensor giving an inaccurate reading

Jon

Wouldn't that cause power to drop off ABOVE 2500rpm?

As above, surely this would restrict power only at high revs?

Possible, but once again higher revs would exacerbate the problem, and it's OK above mid range, poor below (when less air is consumed and partial blockages would have less impact)

A possibility also, but the engine is smooth, returns 45mpg + at motorway speeds of 70mph, and shows no signs of sooting. Do you have evidence to show changing this part has worked for these symptoms?

gearchanges

Yes. The car behaves as though it is driving at altitude, the fuelling is lower and your mpg would not get any worse nor would there be any smoke or soot. The best description I have heard of this is "like driving in glue".

With regards to the air filter or fuel filter, when the engine is at speed i.e. +2500 rpm the speed of the engine would overcome any impediment, air or fuel filter, until they got really bad.

I suspect that the end result is your map sensor going out of tolerance, they are somewhat finiky at best.

PDH

Philip, can I give you a few words of advice.

When you ask people in this newsgroup for advice or help, the last thing the person offering advice in the newsgroup expects is what could be construed as a sharp stand offish attitude to possible answers offered. I was to say the least offended by the tone of voice which came through on your email which was sharp to say the least.

The majory of people who frequent this newsgroup and offer such advice do so quite freely on the provisio that such advice is welcomed by the asking party. The same people also have the benefit of experience, and the results of such experience often help others out with the same issues. For the record, I have driven diesel for many years now, I am au fait with the types of faults and their symptoms which may crop up, for a hobby I work with diesel engines, 15 ton power units, and I certainly get the hump when what credible help I give is questioned because the person asking does not like the answers.

One piece of advice I was given, and I'll pass on to you. Always address an email exactly the same way as if you were addressing the person face to face. Email is very impersonal, and although it may not be your intention to be sharp and to the point, it is easy to send such mail unintentionally.

Rdgs

PDH

Paul, it was certainly not my intention to insult you or anyone else, and for this I apologise (in public, so to speak). I do appreciate the time you spent offering your help freely, I was merely seeking to add clarity to some of your possible solutions, and the sharpness to which you refer may have been due to an attempt to compensate for my lack of typing prowess. For this reason it is very difficult to assume a face to face discussion, as a face to face encourages a dialogue of small portions with regular to-ing and fro-ing of views, in person it would be easy to judge by your reaction to me "questioning" your first possible solution, that you were losing interest in offering advice, and I would either change tack to retain your advice, or cut the conversation.

In conclusion, and because my fingers are hurting, please continue to offer your hard earned advice and try to understand that there are others who have less experience of this medium, but learn quickly.

unintentionally.