my fault turned out to be
related, removed the jack to find the top metel cover badly rusted, then the plastic case had a small amount of water in it, removed the
and found the metel was all white and furry - oxidation, water/alloy. i removed the circuit board and couldn't see a single thing wrong, but still replaced it and it fired up straight away. also had to replace the idle control valve as that was faulty. but after a week of driving the car myself it seems to have behaved itself, so, result!