Hi All,

My clk 230k has acquired a fault. When fired up, instead of ticking over as normal, it's revving up to about 2000 rpm then dropping back down to tick-over, as soon as it drops down it revs up again to 2k. It's as though the accelerator is constantly being pressed.
The frequency of the revving is about ever 2 seconds. Since it's done this the CEL has now pinged on.
It's happened about a year ago and I just disconnected the battery for a few hours to reset the ecu and the problem went away. Tried that this time and no joy.
Anybody any ideas?

A few thing come to mind:

Vacuum issue - check all the vacuum lines you can find.
Pedal sensor gone bad
Throttle body contaminated

Hi,
Just an update. Took it to my mechanic yesterday, plugged in the code reader (of which there were loads of fault codes). Cleared them all so we could start a fresh and see what fault code came up, and resetting the OBD has cured the fault. Not impressed as I still don't know what was wrong.

hmmm I would feel the same, as its strange how clearing the codes will influence the revs? when the revs went up and down, did they settle after you gave it a little rev? My wifes C 180 does this and thats how I stop it.

I wonder if the MAF would cause this ?

Hi,
No, it just keeps on revving itself, even when you're driving. It's as though one sensor is saying it's revving too high and some other throttle control is saying not enough and just keeps going round in the same pattern.

Have you tried to un-plug the MAF? if your lucky and it still runs see if the problem is still there, if its not then it would suggest the MAF's faulty.

PS My number plate would look good on your car !! fancy buying it?

Hi,
The MAF was fine, I fit a new one just to see and it made no difference.

I guess there's a glitch in the software on my ECU.

Thanks for the offer of the plate but I prefer mine as my name's Alex J. Yates.

Hi did you eventually find out what the problem was? I have a 98 ml320 and I am having the same problem.

Just resetting the ecu with a code reader solved it.

I have what sounds like a similar problem with my Crossfire that has a MB 3.2 engine. I've cleaned and replaced the MAF that seemed to fix the problem but only temporarily. I also had a shop clear my codes but the problem comes back and goes away. And it's always on or off - nothing in between and the revving doesn't start or stop while the engine is running. It either runs normally on start up or revs wildly on startup.

When it revs up and down to about 2500 RPM, it's rougher than normal so it doesn't seem to behave as if the throttle sensor is wonky.

Wondered if your problem stayed cleared up after the reset or if it returned and you found another solution.

​​​​​​​Came back a year later but a reset of the ecu usibg a code reader cleared it.

Did you use an app and bluetooth OBD adapter (which one?) or something more professional? Googling for a couple of minutes, it looks like Torque Pro can clear codes but I haven't seen anything about an ECU reset.

​​​​​​​Thanks.