Trevor, firstly I am sorry about not getting back you you earlier to thank you for your advice. Thank you. I have had the coolant sensor replaced (£10 fitted) during the cars service a couple of weeks ago. The stutter is still there but less pronounced and lasts a shorter time. So, there is some improvement but it is not fully rectified. I am now thinking that maybe to choke is not coming off cleanly once the engine is warmed up and my have a look at this. Once again, thank you for the help. Steve