Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Unwanted Acceleration from my 1995 Mercedes S600 V12

Hi. My 1995 Mercedes S600 with a V12 engine has a serious problem with unwanted acceleration. It generally happens when the car is already warm, and doesn’t appear tied to something specific such as the air conditioning. Suddenly the tach needle will start swinging between 500 and 2500 and the engine revs up and down, requiring me to mash the brakes at stoplights, drive unsteadily as the engine revs and backs off, etc. It’s maddening, plus unsafe. The problem then will stop as suddenly as it started. The car will hold a steady idle for a little while, then start the crazy acceleration again. They’ve replaced several electrical parts, including the CTP sensor on the gas pedal, both oxygen sensors and the air injection pump, and this erratic problem persists. Any ideas? Thanks very much! Chuck

I think you need to see a MB service dept. Does this happen when the cruise control is engaged? Is this a “drive by wire” electric throttle? If yes and you’ve replaced the sensor on the petal, then the actuator at the other end of the syetem could be bad. Or, some other electric component is interferring with the drive by wire system sending current to the actuator that isn’t coming from the sensor on the gas petal.

You also want to make sure the floor mat is not interfering with the accelerator.

i wish it was as simple as the cruise control, but it’s not related at all, as it just happens without cruise engaged. likewise, the floor mat is not anywhere near the accelerator. it seems like an electronic issue, as it just starts revving up and down for a long while, then the problem sometimes stops, then starts again. the m-b service dep’t might be my only option.

i wish it was as simple as the floor mat, but it’s nowhere near the accelerator pedal. it seems like an electronic issue, as it just starts revving up and down for a long while, then the problem sometimes stops, then starts again. the m-b service dep’t might be my only option.

The question about cruise control, the extra revs don’t happen when cruise is engaged, leads back to the sending unit on the gas petal side of the drive by wire setup. It is more than a simple switch, it must be some kind of rheostat or potentiometer. Very likely only MB would have these type of parts and tne ability to test the system and diagnose it.

I am thinking 1995 is a little early for a drive by wire setup but you do mention a CTP sensor on the gas pedal,what is this sensor. With the car off can you press the gas pedal and does the throttle on the engine move?

What was the rational for replacing the 02 sensors the air injection pump? was there a seperate problem?

Has anyone looked at components in the idle system or the throttle housing its self?

Has anyone checked for TSB’s related to this problem?

Here’s a possible:

A broken or loose TPS (throttle position sensor) can cause intermittent bursts of fuel from the injectors and an unstable idle because the PCM thinks the throttle is moving.

I vote for a faulty TPS.

Had the car scanned for codes?
What about an erratic Idle Air Control valve? The car is 15 years old and IAC problems are common on just about any make out there.

My aircraft maintenance instructor had this same problem on his wife’s little Mercedes. I believe that it is a 12 cylinder engine also. I forgot how he solved the problem. He went through the dealership at first also … to no avail. But, he is an electrician. He fixed it himself. I will try to find his email address.

I found the email address for the aviation electrician fellow who fixed the same acceleration problem. I do not really have the right to publish this kind of email address. If you wish to send your email address to me, I will pass it on. I will also ask him to type a message here as well. My email is
He was dumbfounded at how dangerous his car was… a Mercedes no less. He loves the car though.

Thanks, I’ll have the TPS checked.

I’ll check this also. Thanks!