i have 1999 ford f-150 4.6 liter and it started misfiring and idling really ruff.?

[Alex]

now it seems to only misfire when i put it under a heavy load and my check engine light is on and it started flashing today when i was driving it. when i got home i turned it off and then turned it back on 5 minutes later and the light was off. i have no clue what is happening can anyone please maybe give a direction on where to start