Re: New issues after head gasket...
Well I'd be betting on some sort of fuel rather than spark problem to begin with, thought it is possible. Perhaps oxygen sensor- they actually do die after a certain time (constant heating and cooling) or maybe throttle position sensor, MAP, something else like that.
As a car gets older everything inside the engine wears out and so allows slight air leaks, thus reducing vacuum in the manifold. This gives the car a signal that it's under more load than it really is, so oversupply of fuel occurs. Falcons already run rich, so this would just make things really bad. Same deal if the TPS is telling the ECU that the throttle is open when it's not.
There's probably other things too, but that's basically all I know.
1987 Jaguar Sovereign - Metallic Green
3.6L DOHC 24 Valve