just to finish this thread off - here's the replacement list - front Oxygen sensor, Mass Airflow Sensor, Throttle position sensor, new spark plugs, new catalytic converter - out of this lot, the new cat made the biggest difference - this car had obviously spent a lot of time idling around in traffic in Japan!
Anyway the piece de resistance is that while working on the TPS, I thought - "I wonder if this throttle is achieving wide open position"?? Answer - no, the butterfly was not quite reaching full open position and, there was a fair amount of throttle slack. So, to adjust this - there is no lock-nut arrangement - there is a metal clip that when removed allows a grooved portion of the throttle cable to be pulled through , you set the required position then re-insert the lock clip and voila - problem fixed - performance no longer an issue!! Shame I have just sold this car and have a 2.5 litre duratec version arriving soon - hope they're easy to work on!!
