Commiserations as these intermittent faults are the worst type, not familiar with the Gems system but I have heard of very similar symptoms being cured by renewing the ignition amplifier situated adjacent the coil itself on my 3.9.

Good luck.


2009 4/4 Henrietta
1999 Indigo Blue +8
2009 4/4 Sport Green prev
1993 Connaught Green +8 prev