HELP! My car revs up to 5000+ upon start up

mercedes-benz
c-class

#1

My 1999 c230k was fine just yesterday and then this morning when I started it the rpm just kept revving up past 6000 in park. so I shut it off and tried again then it did it again so I let it go and it stopped and went back down but only to 1500. When I put it in drive I can feel it trying to rev its self a little. The car also doesn’t respond to the gas pedal well I can push it down and it won’t really do anything just keep jerking and I have to push the brakes extremely hard to stop the car! There is not check engine light either! Help please and thank you!

I think it’s either the Idle air control or the throttle body but I’m not sure. I did take out and clean the throttle body and it didn’t help


#2

One of the regular posters here is a professional mechanic with Mercedes experience, perhaps he will chime in.

But my professional advice would be to shut the hood and have the car towed to the MB dealer or to a reputable qualified independent shop with the proper tooling and experience to repair your car. An unexpected engine rev to 5000 rpm while you’re driving can be a disaster.


#3

I’m hoping not to resort to that just yet and sorry I didn’t make it clear it only happens when I first start it and it’s in park. But thank you I do appreciate it


#4

No idle air control motor on this

It has a very early electronic throttle system, kind of a mix of mechanical and electronic

There’s a motor on the electronic throttle body, and no cable attached there

But there IS a cable going from the accelerator pedal to the accelerator pedal position sensor, which is in the engine bay.

Since you’ve already cleaned the throttle body, I’d say next free thing is to make sure there’s no obvious and/or physical problem with the pedal, cable and that sensor I mentioned

After that, take it in to a shop. I suspect once somebody hooks up a scanner and gets a hold of the wiring diagram for the throttle controls, they’ll figure it out within a reasonable amount of time

If you aren’t able to somehow fix it on your own, have it towed to a shop. Far too dangerous to drive, if you can’t trust the throttle

You said there’s no check engine light, but there might still be some meaningful codes, but ones which are not commanding the check engine light to turn on

My gut feeling . . . without being there and having access to the car . . . is that something is wrong with the cable or that sensor

But don’t go replacing expensive parts just because some guy on the internet had a gut feeling

Are you handy?

Do you have a digital multimeter?

I believe you could easily test that sensor. Since it has a 5V reference, it could be tested as if it were a tps, I would think.

It’s been awhile since I worked at that Benz dealer, but that’s a pretty old car and not that complicated, not compared to some of the newer cars out there


#5

Yeah I am I can test it, and thanks for the response I will be sure to test it. I was kinda thinking it was the cable sensor but wasn’t sure either. But thanks again man I appreciate it


#6

You’re welcome

Please let us know what happens, even if it takes a few days


#7

Will do I am actually away for the week but as soon as I’m back I will look into it.