Could be timing.
Have you done anything to it prior to it starting this? Have you done anything since?
Have you set the tickover in service mode? Don't piss about with it if it's not in service mode as it'll cause what you're describing. Not saying this is your cause, but I couldn't be arsed on one of mine, just turned the idle a bit to make it better, resulted in a barely useable car, jerky, on/off, etc.