Mine NORMALLY ticks over around the 650/700 mark but today it struggled to start and was a little lumpy at first around 500 but it had been -13 overnight once it warmed up a little it was fine, as others have said more info required for a judgement to be given.
Light a little fire under your tank first thing in the morning, then make yourself a cuppa, pour any remaining hot water over the fuel filter, start her up and she'll run like a dream.