devanrwalker

I sure hope it's nothing serious, but I bought a c32 to restore after some vandalism and I have everything pretty much fixed besides one issue I cant pin point.

While driving steady, say 45-50 mph my speed will remain the same but the RPMs will pulse between 1100-1500, I don't think it's the tranny since when I really push it there is no slipping.

Any thoughts?

Gramma_Benz

Sounds like throttle body to me. It doesn't fluctuate at all at idle?

C3Duece

could be the CPS beginning to die.

Lenin

+1 on TB or the TB cable.

devanrwalker

Seems odd to me, wouldn't the TB failing also effect the speed? Or are our cars too damn smart and counters it.

C3Duece

Agreed. Wouldn't OP feel the rpm changes as surging/dieing? Pretty sure C32's are drive by wire...ie no throttle cable.

Lenin

TB may or may not be failing. It's hard to tell remotely. What I'm referring to is TB sending an erroneous voltage to the ECU due to a bad electrical connection. The RPM is surging but the speed is not increasing. The unusual thing is that it would also happen at idle. But not in your case. Do a search on "sneaky ECU reset" and reset your ECU. See if it helps.

"Pulse between 1100-1500" is how I would define surging. When I said "cable" I was referring to electrical cable that connects the TB to the ECU. When was the last time you opened the hood of your car?

C3Duece

Go back and read your post. you said nothing about an electrical cable.

Lenin

Everyone that owns a C32, except you, knows what a TB cable is. And read this. You may find this educational. https://mbworld.org/forums/c32-amg-c...dy-thread.html

Gramma_Benz

he said TB cable, which IS an electrical cable.

C3Duece

wrong...OP didn't know what it was either. Regardless I'm not going to get into a pissing match with the 2 big hero's of this group. I've owned my car all of two months and athough I've still got a bunch to learn I thought I could help out another member.

OP..I hope you get the issue worked out

devanrwalker

I open the hood of my car daily, I have done fix ups as in spark plugs, front SAM, led lights, tranny fluid change, oil change, secondary ic pump, alternator, coolant flush, child seat restraint fix, aux to tape deck mod... basically the works, I am a pretty good mechanic that had a few 11 second cars and did this all in under a month but I have never worked on cars where half the items require a flash of the ecu or programming to this extent. (would love to buy a star system, would have a hay day but need to save up)

Ill check my cable to see if any of it is damaged and will work on that first.
Already did sneaky ecu reset and also battery reset. If it fixes it, it doesn't last long. Ill check to see how fast it comes back if it even fixes it temporarily.

All in all for a car with total vandalism, the exterior now is completely fixed and all the interior besides the back seats have been fixed.
The thing was knifed on every piece you could think of. So far I think im making good progress in this restoration, just a few things I didn't see coming.

Lenin

The comment about opening the hood was not directed at you.
This surging problem is one of the more difficult to figure out. The ECU monitors the Throttle Position Sensor, Cam Sensor, Crank Position Sensor and bunch of other parameters, then calculates the duration the injectors are open (injector pulse width). And fuel through the injectors drives the RPMs. So, as you can see, it can be a number of things that may be contributing to your issue. Before spending any money, see if you can connect it to the STAR system and see if there are any codes (including hidden codes). That may point you in the right direction. Good luck.

johnng117

I had this problem, after trouble shooting it was not the TB, it is cable related.
I changed the engine harness which includes the TB harness and solved everything inc esp problems.

C3Duece

I remember reading a thread awhile back where users would zip tie the plug connector tighter into the TB which fixed some surging issues which would be considerably cheaper/easier than replacing harnesses. Worth a try at least.

devanrwalker

Sadly there is no Star system in my area for under 120 an hour, which all shops charge at least an hour.
I reset the ECU again and tried the zip tie trick, but I really hate having that plastic wrapped on there.

C3Duece

did zip tying that plug into the harness fix the surging?

johnng117

Temporary fixing it to sell then zip it, if your intending to keep it for a long time then think about changing the harness.
The Harness causes a lot of problems and causes the ECU to throw faults which are not true.
Because the harness is causing problems intermittently the ECU never knows its a harness problem.

djdirty76

Hi. Just something for you to think about. I had similar problem. Rpm were all over the place. Tried Ecu reset. Throttle body cable cleaning and zip tie. So finally decided to get a throttle body and a new accelerator pedal assembly. I was hoping that it's not the wire harness since it's the most expensive thing. Turned out my throttle body was fine. It was the accelerator pedal. Bought one of eBay of a 2005 cclass. If you wanna know the part number let me know. IM at work right now and don't have it here. Anyways try to maybe ask someone with a c32 in your area if they were nice enough to switch accelerator pedal with you to try if it is the problem. It takes 5 minutes to remove and reinstall. As soon as I put the new accelerator pedal inn car the problem went avay. I reset the ecu and seems its great now. I'm left with a spare throttle body for a 2003 c32 that I will sell. Anyways good luck with your problem.

macbryanie

+1 I have had this on and off for a while, after eliminating other causes it came down to the TB cable, my fix was some stabilant 22 http://stabilant.com/techt02h.htm
(however I went ahead and bought the replacement wires regardless) refer here for more info https://mbworld.org/forums/c32-amg-c...y-p0120-3.html
hope its a quick fix , BTW if it wasnt for "2 big hero's of this group" and alot of others on forum I would frowning in a Honda CRV each day to work.

devanrwalker

Still kind of the same symptoms with the zip tie trick and ecu sneaky reset. I think the pedal might be the culprit though, since this doesnt happen at idle. Any way to test that before buying a new one? I dont know of any C32's in my location to temporarily swap it out.

Gramma_Benz

You still haven't pulled the codes yet? You don't need STAR to pull codes. I have an app on my phone that does it. However, my mechanic's code reader catches some hidden codes that my app doesn't capture.

Either buy a cheap one for $40 or any shop can do it. That is what will point you in the right direction.

devanrwalker

I pulled the codes with Torque and its clean, I am trying to find a way to get a better reader to show me everything that's hidden.

Gramma_Benz

Yes, my hidden codes pointed more towards the TB.

joc

Hello just bought 2002 C32 from another member with 136,000 miles runs good on highway, but the following is happening
when at idle surges between 1000-1200(like shunting)
rev the car up and it only comes back down to 2000 and then slowly comes back to 1000-1200 again shunting
Put in gear and drops to 800 rpm and drives okay
Stop and re start the car and it goes to a nice idle at 800 rpm.
Rev iot up and goes back to 1100-1200 shunting again .
Do I look at the pedal first? any other ideas
Thanks