Heinz, Sospan,
Thank you again for your input. Brett Syndercombe at BHM has also been very helpful and has contacted the factory too on my behalf but they had nothing new to add. I am experimenting: Looking back at the service sheets before I bought the car shows that this front bank sensor was changed before at around 4000 miles. I changed it at 8000. My experiment was to use an extender to remove the sensor from the exhaust stream and drive to Toulouse and back. There was a noticeable change in that; the engine ran at 2000 rpm on start up and quickly settled down to 900 rpm, Before it would run fast for at least five or six klms and it would sometimes run fast at odd times. That stopped completely. The engine management light did not come on at all. Everything operated as normal, smooth running, strong acceleration, 38 mpg. Next I removed the sensor and extender and replaced them with just the old sensor I had previously removed at 8000 miles. This one had been soaked in petrol and had been sprayed with contact cleaner and left to dry overnight. So far the. OBD reader shows no codes. It remains to be seen how long this lasts.
Sospan, You doubt that the MAF is at fault and I tend to agree as there have never been starting issues, or hesitation under load or acceleration.
The exhausts are not blackened which would be the case if it was running rich due to excess fuel being fed as a result of perceived lean running. I cannot detect any leaks from the exhaust, or from vacuum pipes. The CT (MOT) did not pick up any aberrations.
Stay tuned I guess.
