2000 Volvo S80 sporadic bursts of thrust

I have a volvo s80 t6 twin turbo with 170k miles. Whenever I start my car and hit the gas the power is usually a steady flow depending on how fast im going. Over the last few months as I accelerate the speeds jump up and then the power drops for a second and then for no reason goes back up to the normal acceleration. My check engine light came on a few days ago and the mechanic indicated it was something like a misfire in the top end of the engine. I replace the spark plugs and am still having the acceleration issue. I am wondering if the sudden acceleration is related to the check engine light and something like a sensor or electrical in the top end or if you think they are totally unrelated? Any help you could provide would be great