Finally got some ECU errors come through with my long-standing poor mpg. "Lambda (Oxygen Sensor) Regulation - Control Limit Not Reached - Intermittent" Any ideas? The plugs are a little black, not normal. I've tried an ECU reset and training procedure. The blue sensor was replaced a couple of years ago. With logging on VAG COM, it warms up beautifully in a sensible ramp from cold to 85C. The lambda readings start changing at 60. The lambda was faulty once before and replaced last year and appears fine now - 0.95-1.05 on VAG COM when idling. The weird thing is the range of ADAPTATION values for
