You might have two problems here; the misfire and stalling as well as the car not turning over on the key sometimes. A diagnostic check with either an auto electrician or somebody who’s an expert in Fords of this type and vintage should be your next step.

The problem could be something wrong with the fuel or ignition system, or even something fundamental like a poor earth connection somewhere on the car. Modern cars can show up some really odd, intermittent problems thanks to a bad earth. But don’t rule out other obvious stuff like the car’s battery condition or the leads that connect it to the rest of the vehicle.

A faulty body computer is the most likely cause of this behaviour. It’s a common enough fault with this series of Ford Falcons and it often requires the body computer to be replaced as well as the ignition keys to be re-coded to the new computer. Unfortunately, it’s not a cheap fix, although you could try a second-hand computer from a wrecking yard. There’s every chance, though, that it could develop the same problem sometime in the future.

It sounds to me like a fault with the transmission ECU. By turning the engine off and restarting you are rebooting the computer, which suggests it's a fault with the computer.