I had a similar problem with the Roadster.
In the end I had to buy a new Ford air flow sensor, cleaning didn't help.
Once the new one had been fitted I had a close look at the old one. They work, I understand, by measuring the temperature drop across the heated wire caused by the air flow. The old one had what seemed to be almost glazed on gunge at the two ends which I think acted like an insulator.
The BMW V8 in the Plus 8, at the same age must use a different way of measuring air flow, the MOT results last year gave a Lambda of 1.006, the max limit shown is 1.03, as mentioned above.
So why don't they use 1.05 if that is in the D&VSA documents?
A perfect Lambda result is 1.000.
The CO was 0.03 %, limit is 0.2%
Hydrocarbons 12ppm, the limit is 200ppm.
So the engine seems to work as designed.
