Volvo S60 170hp detonator in 5th cylinder

Moin, I drive a Volvo S60 built in 2000 with the 2.4l 5cylinder engine 170hp. After driving on the highway with a time of about 160km/h on Wednesday morning, I discovered an error message “please drive slowly, engine maintenance urgent” and the MTK was blinking at the yellow. After driving down from the highway, I just noticed that something was wrong, giving gas no real power and yes sounding like a trecker in idle. When I was at home I pulled the plug from every ignition coil, cylinder 1-4 I could detect a change in the engine run, at the 5th cylinder act nothin’ when I pulled the plug, so on screwed up and looked and fact the spark plug was heavily rusted and lacked a little bit of the candle. Well, new candle and certainly half new ignition coil was ordered and built in. Unfortunately without success, old ignition coil also tried No success, after relatively short time the candle was again full of gasoline and oil? So the candle would not have to be wet?