rlddlr53

At Idle, my C55 needle on the tachometer or RPM gauge, slightly moves.

My friends star computer shows it fluctuates between 625-650. No Codes, No CEL, No misfiring, engine is running smoothly. TB has been cleaned, MAF has been replaced. Same issue still occurs.

Any ideas? The movement of the needle is very slight but my previous c55 and clk55 did not do this.

ghiaguy

mine does this too- I think people have solved it with a fresh voltage regulator...

rlddlr53

Voltage regulator replaced today with new OEM Mercedes battery. Car drives great and still has the small tach needle fluctuation at idle. MB star computer shows fluctuation of 625-650. Under smooth engine running, all cylinders are running within spec.'

Any ideas anyone?

ghiaguy

Funny, I replaced my voltage regulator this Saturday (finally) and I am a bit underwhelmed by it too. I still have an occasional minor shudder at stoplights.
Worst is it didn't fix my SOS teleaid error that I've had since I bought the car. Tried STAR "not present" trick, looked for trunk splitter, and heard this might work. No dice.

Duncan64

i've noticed quite a difference by replacing all my breather hoses (4 + adapter) and my engine has never been so smooth! At lights i almost dont even know the car is on. My RPM gauge does not twitch when its idling i believe... but i haven't paid that close attention i guess.

I replaced my breather hoses in an attempt to figure out why my oil keeps getting blown out and leaking everywhere even after fresh seals on the valve covers and breather chambers. So far so good....

frejo

My rpm gauge and speedometer fluctuates very slightly at speed. Does this indicate that my voltage regulator is going bad?

mgiannetto

My C55 does the same thing, but only at idle - and even then, only infrequently. I'd say I've noticed this for the last several years.

I have often thought maybe some bad gas from time to time (I only run 93 octane premium by the way)? Don't know for sure.

Have not replaced the voltage regulator, but did put a new battery in last year. I don't think that made any difference. My car has low miles on it (37K) so I thought maybe the fact that it is not driven all the time or extensively is another contributor.

It's really so minor that I really don't give it much thought even when I do feel it happen.

gwin

It's called idle hunting, mostly due to sparks/coils, can sometimes be MAF but unlikely. All cars have this issue.

Viper98912

I thought this was normal in all cars, including all the ones I've owned

MarcusF

It is normal in all cars. If the OP looked at the voltage output from the primary O2 sensors, he'd be shocked that engines run as smooth as they do. In all cars, the O2 sensor reading constantly swings between rich and lean whenever the ECU is in closed loop mode. In closed loop, when the ECU determines the engine is running rich, it leans out the mixture. As soon as the ECU determines the engine is running lean, it enriches the mixture. This happens the entire time the car is idling (closed loop mode). The engine speed varies as the air:fuel mixture is changed.

rlddlr53

Its only a slight annoyance on my end. The car drives great otherwise. I am actually looking to sell it right now.