3rd cylinder missfire

[kostasbmw]

i own a 2004 e83 petrol 2000cc and i m happy with it

at 180k km i converted to lpg now i m at 380k km

i get a engine check and the reading was missfire at 3rd cylinder..

no power loss but at idle is a little shaky.....not stable

so where di i start.....coils , plugs ???? thats the easy part

after that i guess i need a pro reading from BMW but the expense would be

some money...lol

i forgot to mention that now i run it on petrol because work covers the expense....

thanks for any advice given