Thx Rick. Replaced all six coils and six plugs with genuine volvo parts. I will check for intake and exhaust leaks.

My XC90 has 211,000mi and currently has the p0420 & p0430 codes set. This problem started when the coil for cyl #2 experienced a meltdown. Three miles from the house I limped home but I know now I should have pulled over and shut the engine down. That week I replaced all coils and spark plugs with ...