C230k Tach and spedometer pulsing in sync with cruise on after sparkplug and starter
 

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?

I think the codes are the big clue, if they weren't there before. I am not familiar with those codes. You may have forgotten a connector or hose, or maybe a hose cracked, while you were doing the other work.

I checked back over all connections twice where i replaced the spark plugs. The only thing unplugged with my starter were the two wires that went to the starter.

I looked up those codes and they point to the intake temperature sensor although the codes are somewhat generic. I don't know how that would make the speedometer and tachometer have a slight rhythmic pulse to them with the cruise on. So far that's the only time i notice the pulse. At Idle and at speed they seem to be fine till i hot the cruise.

Putting in the starter, only two wires were touched. The two belonging to the starter which was put in from below the car. While doing the spark plugs, i only moved the air pump solenoid to the side without disconnecting it. I went back over the the whole area and saw nothing disconnected. I checked the vacuum and its fine. No leaks.

P2020 and P2042 mentions the air intake temperature sensor.

Reason For P2020 Code
The reason of P2020 OBD-II Engine Trouble Code is Ambient Air Temperature Sensor Circuit Low.


P2042 OBD-II Diagnostic Powertrain (P) Trouble Code Description
P2042 engine trouble code is about Glow Plug/Heater Circuit 'A' Malfunction.
Main reason For P2042 Code
The reason of P2042 OBD-II Engine Trouble Code is Ambient Air Temperature Sensor Circuit Low.