surge

Started running a 50-50 svo derv mix on wednesday & today I experienced what I can only describe as a surge in revs when stationary at 1200 rpm it will rev to 1500+ does not stay there it drops off to 1200 then back up to 1200 odd, I have done nothing to the car recently other than the fuel mix, first thoughts that the turbo was acting up ideas anyone thanks
Dev

Try a new fuel filter. Something similar happened to my car when I stuck veg oil in it. Should sort itself out.

Cheers Andy I will start with that
Dev

Just an update, filter changed and the swamp removed from the sediment trap pull like a train now
Dev