It appears I have some sort of air leak / O2 sensor problem with my Mondeo ST220. The engine management light is on and the computer says both banks are running lean. I cleared the fault but it came back after 60 miles.

Is it advisable not to drive, whats the worse that could happen? I understand it could run a hotter, but water temp has remained the same.

No apparent loss of performance / smoothness / mpg.

Thanks in advance.