Mercedes Benz E 320 1997 What causes it to idle rough?

Question

Coil for number 4 cylinder was replaced.  It runs better but still Idles rough.  The check engine electronics light came on before and after the coil was replaced.

Answer 1

Ignition cable , will cause the vehicle to run rough, and depending on mileage having carbon build up on the valve will also cause a rough running condition, use a fuel treatment added to the fuel tank to lessens any carbon build up