Two weeks ago I changed the spark plugs in my 2005 C230 Kompressor. Prior to changing them i never saw fluctuations in the speedometer or tach with the cruise control on. In fact, the day before replacing the spark plugs, while using the cruise control, i saw no fluctuations. Today was the first time using cruise control since the spark plug change and changing my starter motor today and noticed a slight "pulsing of the mph and rpm that seemed to match up. I would say they are moving about the thickness of the needles or slightly less. I cannot feel any difference while driving. I also do not notice any pulsing (fluctuations) of the speedometer or tach when the cruise is not on.

The cruise can be set and speed increased or reduced from the stalk.

Its dark now and have not run a battery of tests yet.

I have no dash warning lights on and scanned for codes. I had no codes just a couple days before putting in a starter.. Now it shows a p2020 and p2042.

The conductor plate was replaced back in November so there is a new speed sensor.

I was thinking it is vacuum related. When i pulled the plastic cover off the top of the engine to replace the plugs i had to move (not disconnect) the Air Pump Solenoid Valve to remove one of the coil packs. I noticed that the vacuum lines under that cover did have allot of oxidation on them and turn your hands black just touching them.
I did buy the car used last year and did notice that many of the thicker vacuum lines look about new.

Is there anything that i should be looking for specifically trying to diagnose teh pulsing of the speedometer and tach with the cruise on?