What's in a name, by any other name would smell as sweet?
Many thanks for your advices gents...it still runs OK round town...just the plateauing on the motorway to contend "so far". There still has been no Engine MIL illumination. Only the OBD indicated presence of a fault code therein that I cannot get to read.
Worry that mentioned "over boosting" the turbo might blow it totally...is this a possibility?
There is some sort of valve on the turbo that I believe Mr Doom mentioned might be coked up...is this accessible and perhaps an easy job to clean? Is this an air or oil valve?
So as opportunity and funds permit its going to be;
1. Oil Flush followed by oil change & filter. Replace Air filter
2. If I can get the vehicle jacked high enough to clear my stomach get under and check those turbo hoses.
3. Try to get DIY OBD2 Elm 327 plug code reader working properly with laptop and see what the ECU is saying
4. Failing to get DIY OBD2 working take it down to main dealer for opinion and break open the credit card again...
I just know that sods law will kick in here and crock things up just before the "fortunes" awaiting the streets at Christmas, just why is "Sod" always hanging around the Taxi trade...if he is no good at nowt else he could always try as for LO! :O)
Will keep you posted if a cause is found
Be Lucky out there