Thank -you for your reply. I did replace the O2 sensor last night because the Benz seemed to be running rich as well. I definitely noticed more take off power, but the smoke out came back again.
The old sensor probe was covered in black residue and I noticed oil seepage coming out the the manifold pipes that connect together right before the O2 sensor. Will pull the sparks plugs as you suggest. Are the value guides difficult to adjust/replace? What would I be looking for? Thanks!