Since your car has been running on Techron for awhile you can rule out dirty injectors as a cause for the rough idle . I get lots of rough idle complaints on M112/113 equipped MB's, especially after about 50K. If it's only slightly rough there won't be any fault codes. A new set of ignition wires makes them run like new again. The wires aren't cheap though, so make sure you check the obvious stuff before replacing them. Keep us posted.