I have a 2001 Volvo S40
Last saturday, while driving in the highway it just randomly start misfiring, like around 50+ mph

like itll shake a bit and then run fine. The check engine light finally came on during a misfire. Had a mechanic check it, and told me its a misfire in cyl 4.

i had all the sparkplugs changed. (was told old ones were good)
changed the coil for cyl4
changed the plugs on top

its not misfiring as bad anymore, like its not very noticable unless i like give it alot of gas at like 50 or 60 mph.

anyone have any idea what it could be?

 

Maybe the other coil is bad now or the wires.

 

If it has good spark, next step would be a compression test if it's still dead.