This sounds like an Aussie EF Falcon. Check the connection to the PCM. There should be a plastic cap over the top of the PCM (Power Train Control Uint) located under the dash to the left of the glove box against the A Pillar. From my own experience moisture gets in between the plug and the contacts to thee PCM. Ign key out, Remove the cover. A star point screw holds the strap securing the PCM. Use a 10mm spanner to loosed the plug and clean the rubber seal and the seal at the bottom of the EECV PCM connector. Don't spray any lubrication oil. Leave them dry and re-enstall . NEVER Undo the PCM plug with the ignition ON or on ACC as it could damage the PCM