I'm a newbie here and I've searched the threads but nothing seems to directly relate to the problem I'm having.

So...

I had an engine fault code which turned out to be a burned out plug lead and arcing out spark plug on cylinder 6. I changed the plug replacing it with what was in there previously, an Autolite 104 gapped at 44. I disconnected the battery and let it sit for 20 minutes but when reconnected and started up the engine just will not run correctly. It's running roughly and won't reach the correct idle speed.
I've checked all of the other spark plugs and leads and they are in tight and in the right places.
I can't for the life of me figure out what's gone wrong with just a plug/lead change! The plug may not be what Ford say it should be but it had run fine with it before..

Any ideas guys?!!