my neighbours astra;
misfire-intermitant.
cause (took me ages to find it, after garage had done plugs, coil pack, sensors then gave up. ) : the connector to the end of the coil pack had a slightly bent pin in it..
just the movement of the engine starting would make the misfire disappear and i only found it by gently moving the connector and wires slightly, to much and the fault wouldn't show.
dont cut the old connector off (if this is the cause.) just solder a new one in parallel .then if it turns out not to be, you still have the original.