Saxo 1.1 1998 Surging

[carl]

my wifes Saxo will only tick over when you press on the throttle . It also surges , loosing about 15miles an hour then returning to the original speed in a pulsing fashion. It does this about every 3 or so miles. Have changed .coil leads plugs temp(to ecu) sender lambda probe fuel filter. Drained about half a litre of petrol into a bottle. No fault light on dashboard. Checked and cleaned all connections. Checked all vacum hoses. Wonder if fuel delivery pressure is correct but not sure how to check. The car has Bosch single point injector and it has done 29000 miles. Meant to add the stepper motor moves in and out sufficient to just keep car from stalling when hot. Help!!!