Replaced one of the coils @ 102000 miles then a.

Replaced one of the coils @ 102000 miles then a wk ago ck engine light came on and it seemed to be idoling rough and then 2 days later it went off and car seemed to run fine. Now it's back on again and every time I start the car it surges hard, it doesn't matter if the engine is cold or warm and it's only at start up. I let the engine idol until it surges before I take it out of park because if I dont it will surge forward/backward and I have to step on break. Other than that it is running fine. I have not had the major service done(belt water pump etc.) As I was planning on selling it. What do you think is happening? By the way it is S60 2.5T Turbo. Thank You !