More idle/ignition system problems...

[Hunter]

Guys you might remember that a couple of months or so ago I posted about my 96 EL Falcon idling like ИИИИ, which it still does. Well anyway its developed another interesting problem. When I start it, sometimes it will start normally, that is it will kick over smoothly and everything is aok. But occasionally it will kick over with a huge THUD and it does not sound very good at all. Its like start start THUD and the whole car feels like it just got rammed up the ИИИИ by a truck. Now, the thing is, it doesn't take a lot of effort to start and either way it still starts easily but this thudding noise is really concerning me.

Any ideas on what it might before I have yet-another-go of finding the fault? I don't really enjoy pulling the ignition system components out (especially the coil or the distributor for that matter!), so I'm hoping to get some ideas of what it might be before I start fiddling.

If anyone has some ideas on what this thudding is I'd appreciate it. BTW it doesn't do it when you switch it off either, it just stops like it always has.