2000 C280, 77K miles... running rough, engine obviously misfiring, check engine light illuminated. Decreased performance and increased fuel consumption was noted in the weeks prior to the CE light illuminated.

Initial fault code check revealed P0300 & P0302. Renewed cylinder # 2 ignition coil, with no change in performance. Rechecked codes: P0300, P0302, P0306 present; data stream revealed misfire rates of 57.88 for both cylinders. Replaced # 2 coil again with known good coil and renewed cylinder # 6 coil; renewed # 2's plugs and plug wires, also plugs for cylinders 1 & 3. Check engine light still illuminated; recheck revealed P0300 & P0302, with 57.88 for cylinder # 2.

Ran a can of LubroMoly fuel injector cleaner in case # 2 injector was fouled and rechecked codes: now cylinders 1, 3 & 4 show misfire codes, with rates approaching 57.88. Cylinder 2 now shows a misfire rate below threshold, but misfire event counter was twice observed to rapidly rise to 99 but then could not be repeated. Misfire event counter for other cylinders remained at 0. Problem intensity appears to be variable, since driveability can be poor at times and at other times normal.

Whats happening here? Should all coils be replaced or is something else responsible for this increasing rate of misfiring?