what year is it mate,its just that some of the later ones,quite late infact,had electronic throttle,obviously you'd know by looking at the pump,but weren't sure weather you knew what you were looking at,no offence,lol,dont know your mechanical knowlege,they do play up,or it could be the electronic govenor on the pump,or like the man says,could just be a slack cable if its below certain year :-k