If it is genuine misfire I would say it is the quality of the fuel. But OK I do not know what youre driving habits are so this is my best advice.
What happens is if you use to low an octane say 87RON and you kick it in the guts it knocks and pings and sounds horrible right? Not all gas is the same my friend. I currently use 93RON Shell gas and I was previously using 87RON Mobil then 93 RON Mobil and switched to Shell which cured my previous knocking sounds on full throttle.
Also older cars may need higher octane gas for a number of reasons if you post tommorow I can tell you more. It has got to do with carbon build up and compression and volatility of the gas and other parameters.