Recently purchased my Volvo, it had just had the engine swapped. The check engine light came on after a couple weeks, to make a long story short, we changed the spark plugs and found the wells full of oil. The oil cap had been leaking- replaced and cleaned all this up and then got codes for misfires in cylinders 1,5,and 6. We replaced coil packs and codes went away. We went on a long road trip and car was working fine, speeds of 70-80 mph on interstate, when decelerated to enter city limits car immediately started misfiring and running terrible, cylinder 5 misfire, traded out spark plug, then coil pack and ran fine for another 200+ miles, then when decelerated again had same problem. Just traded coil pack with another cylinder, then got an OV?VO? code- cant remember exactly. But then car ran great the 700 miles home- what could be causing these misfire codes?