Here is a weird one - I have a 99 disco II with 107K mile, the oil was low so I added 2 quarts of oil, and it put it just above the full line. and after that I got the CEL and these codes:

P0307 cyl 7 misfire detected
P0300 Random/Multiple Cyclinder Misfire Detected Pending
P0307 cyl 7 misfire detected Pending

question is can over filling the oil cause this or is this a simple plug and wire replacement issue (new plugs and 8mm wires 1.5 years ago)

 

That is a weird one, I don't think it's related to the oil though. Try pulling the plug on that cylinder and see what's up. Look at the plug wire for corrosion inside. See if the plug has any sign of coolant in the cylinder. Good luck, hopefully it's not a head gasket!!

 

Have you done your head gaskets yet? did you check the consistency of the oil that was in there? did it look like a milkshake? did you pull the plug on cyl 7 to inspect it ?

 

Head Gasket was done last year at 102K, oil looks good (no milk shake) havent pulled the plug yet......the plugs are about 2 years old though.......

 

It wasn't/can't be from adding oil, if for no other reason you had a pending 307 indicating this has been going one for awhile.
Start checking your fluid on a more regular basis, that is ridiculas to have your oil down by 2 quarts and will kill your engine with time.

 

Is the oil cap on tight and the dip stick back in? If either of those are loose or missing it will run poor.