HI NIGEL, MIGHT BE WORTH CHECKING THE INTEGRITY OF THE CRANK ANGLE SENSOR SIGNAL,IT MAY BE SCATTERING DUE TO A SENSOR FAULT OR THE TARGET,IF THE ECU CANT DUE THE CORRECT NUMBERS COUNT IT CAN DO STRANGE THINGS,CANNOT REMEMBER IF THIS IS THE ENGNE WITH A PHONIC WHEEL ON FRONT PULLEY ?. TREVOR...