CEL Warning Light!

My CEL light came on Tuesday morning and had been on since, although everything seems to be running as usual, the only thing i have noticed is that when stationary the rev limit seems to be set at about 2,500!? As soon as i get moving the rev limit returns to normal. This may have always done this but I haven't noticed before though.

I have already checked that the Brake lights are working, and i have re-fueled from a different petrol station since and the CEL is still lit (I had CEL before and the garage told me it was "Fuel Quality Sensor" which went out after re-fueling).

Anyone got any ideas what else I can check before taking to a garage?

(It's a Skoda Superb 2.0 170 TDI 4x4 in case that helps)

Thanks,

Mark