A problem starting my 1.8 L NA

  1. My model of MX-5 is: NA 1996 , 1.8L
  2. I’m based near: __Kettering Northamptonshire
  3. I’m looking for technical help or recommendations on: __I started my MX5 easily first turn of the key, drove about 500 m the car lost power and stopped.
    Now when you turn the key it try’s to start but splutters and dies then the security light comes on and stays on until you turn off the key and remove it.
    However if you remove a spark plug it will start on 3 cylinders and chugs quit happily. I have removed both plug nearest the radiator and the on behind it and with each removed it will start, but not when you put the plug back and connect it.
    Can anyone offer any suggestions as to how and why his is happening?

Derek