Firstly I'm on MSD wasted spark.

Has anyone ever had an ignition amp break down due the heat in the engine bay? I've problem where if the car is sitting idling for a long time (15+ minutes) it'll go onto two cylinders. If you open the bonnet/drive the car the fault clears, so it's down to the hot air trapped in the engine bay.

The coil pack is only a few hundred miles old. One of the ignition amps is a few K miles old, but the other is the original that was on the car and I've not replaced it since I've owned the car (2007).

The only things i can think of that would cause this fault are one of the ignition amps plying up when hot, or once side of the coil pack going faulty.

Any other ideas?