weird surging engine
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
weird surging engine
Long story, my CL is running fine, i drove it from Germany to home without any troubles...ach Autobahn 
but few days later from a sudden it started doing weird things with this annoying waves.
So it got it's power, idle is smooth and fine, no errors detected when scanned but over 1000 and under 1300 rpm the engine make a kind of waves revving and slowing down on it's own.
At speeds above it's probably "hidden" while accelerating and nothing can be noticed.
- cleaned a lot of old oil and grease crap on the valve covers and down to spark plugs
- I checked vacuum lines
- removed the throttle body for a cleaning, removed the plastic cover from it and no oil contaminated tracks nor dust or other crap.
- changed spark plugs
- replaced MAF
- replaced valve cover gaskets
- running with or without air filter, same results
- Gas pedal reset
- Left Throttle body with contact on, engine stopped, making it's own business to reset
Later i tried to spray carb cleaner and noticed some engine variations while spraying it at injectors feet.
- changed all seals, they were some in bad condition, probably the reason of engine changing idle while spraying carb cleaner
Still the same, now i don't know what to search for.
Emissions failed at it's first inspection and at cold start, runs rough, i noticed a suction noise in front of the engine, just as it tries to get more air or like a restricted air intake, nearly stalling then revving a bit and so on but i can't figure from where this suction noise comes.
but few days later from a sudden it started doing weird things with this annoying waves.
So it got it's power, idle is smooth and fine, no errors detected when scanned but over 1000 and under 1300 rpm the engine make a kind of waves revving and slowing down on it's own.
At speeds above it's probably "hidden" while accelerating and nothing can be noticed.
- cleaned a lot of old oil and grease crap on the valve covers and down to spark plugs
- I checked vacuum lines
- removed the throttle body for a cleaning, removed the plastic cover from it and no oil contaminated tracks nor dust or other crap.
- changed spark plugs
- replaced MAF
- replaced valve cover gaskets
- running with or without air filter, same results
- Gas pedal reset
- Left Throttle body with contact on, engine stopped, making it's own business to reset
Later i tried to spray carb cleaner and noticed some engine variations while spraying it at injectors feet.
- changed all seals, they were some in bad condition, probably the reason of engine changing idle while spraying carb cleaner
Still the same, now i don't know what to search for.
Emissions failed at it's first inspection and at cold start, runs rough, i noticed a suction noise in front of the engine, just as it tries to get more air or like a restricted air intake, nearly stalling then revving a bit and so on but i can't figure from where this suction noise comes.
Last edited by Rkraft; Mar 1, 2023 at 02:00 AM. Reason: add of information
Super Member
Joined: May 2021
Posts: 554
Likes: 150
From: Netherlands
CL 600 '00 5.8L V12
You are not going to solve issues with ELM327. I've got it and it's fine for quick scanning of codes.
DAS is being refered to as SDS, Xentry or STAR. It being the official diagnosis tool that Mercedes workshops use to diagnose cars. Without this tool, you'll only read generic fault codes (as per ODB2), not the Mercedes internal fault codes that will tell you the whole story
DAS is being refered to as SDS, Xentry or STAR. It being the official diagnosis tool that Mercedes workshops use to diagnose cars. Without this tool, you'll only read generic fault codes (as per ODB2), not the Mercedes internal fault codes that will tell you the whole story
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
Thank you for the advice, i was thinking that no OBD errors was meaning all is fine.
So at least it lets a chance to find out more errors with this tool.
I watched quickly on ebay to find a C3 multiplexer and the software, any laptop should do the job.
still i didn't noticed where to plug the round cable, didn't saw something like that in the engine bay
So at least it lets a chance to find out more errors with this tool.
I watched quickly on ebay to find a C3 multiplexer and the software, any laptop should do the job.
still i didn't noticed where to plug the round cable, didn't saw something like that in the engine bay
Trending Topics
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
Slightly added tension on contacts by raising them up and kept in mind they must stay aligned compared to horizontal surface. It should compensate the eventual gap left by years of use. Tracks are fine, there are no groves on them. So i'll try that tomorrow morning.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
Thanks, not yet, they are a way expensive.
Step by step, i'm trying to solve the issue, so far took parts from an old clk to check if any changes but no luck. My AC was not running as well and before i resetted it, i unplugged the wrong connector corresponding to the ABC pump and fluctuating stopped at once but then, of course the dashboard displayed something in german with red light 😁
It says NEIN !!!! VERBOTEN, go play touching something else 😆
So maybe, due to less effort to give, engine stopped fluctuating but this doesn't mean it is the real trouble. Torque needed to make ABC pump work simply put the engine trouble in outline, well i hope.
Step by step, i'm trying to solve the issue, so far took parts from an old clk to check if any changes but no luck. My AC was not running as well and before i resetted it, i unplugged the wrong connector corresponding to the ABC pump and fluctuating stopped at once but then, of course the dashboard displayed something in german with red light 😁
It says NEIN !!!! VERBOTEN, go play touching something else 😆
So maybe, due to less effort to give, engine stopped fluctuating but this doesn't mean it is the real trouble. Torque needed to make ABC pump work simply put the engine trouble in outline, well i hope.
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
I remember that one or two times, there was no surging, just as if something in relation with wiring or else started to work as it should but after driving few kilometers, again that horrible variation when coming to a stop.
Now that i think every possible thing to help engine turn as it should has been done, have to search something else. The ABC pump connector removed stopping that erratic rpm makes me think that the reason is not in vacuum leaks or fuel delivery. I don't know what this connector on top of pump is for but if it drives a sort of clutch releasing pump then, this means the effort at idle for the pump is out of normal range it was designed for.
I have an issue left aside, i have a red brief message when driving on bumps. I planned to repair that later, seems i have to take action to resolve both troubles.
It's frustrating to see a brand like Mercedes-Benz be worse with hydraulics than Citroen with their DS and CX built in the late 60's. Citroen pumps were not that tricky and rocket science to raise a car on 4 hydraulic spheres.
I can't even remember they were filters on micron range, DS and CX entered in Paris Dakar in desert of Sahara and elsewhere in Africa and hydraulics didn't failed.
Well that's life, now i have a complaining hydraulic system maybe because a mosquito pooped on fluid cap or wherever else 😆
Next trying to find faulty things in hydraulic circuit and no i don't want coilovers. This car was designed to work with it's own system, so it'll stay as it was built.
Now that i think every possible thing to help engine turn as it should has been done, have to search something else. The ABC pump connector removed stopping that erratic rpm makes me think that the reason is not in vacuum leaks or fuel delivery. I don't know what this connector on top of pump is for but if it drives a sort of clutch releasing pump then, this means the effort at idle for the pump is out of normal range it was designed for.
I have an issue left aside, i have a red brief message when driving on bumps. I planned to repair that later, seems i have to take action to resolve both troubles.
It's frustrating to see a brand like Mercedes-Benz be worse with hydraulics than Citroen with their DS and CX built in the late 60's. Citroen pumps were not that tricky and rocket science to raise a car on 4 hydraulic spheres.
I can't even remember they were filters on micron range, DS and CX entered in Paris Dakar in desert of Sahara and elsewhere in Africa and hydraulics didn't failed.
Well that's life, now i have a complaining hydraulic system maybe because a mosquito pooped on fluid cap or wherever else 😆
Next trying to find faulty things in hydraulic circuit and no i don't want coilovers. This car was designed to work with it's own system, so it'll stay as it was built.
Last edited by Rkraft; Mar 5, 2023 at 01:15 PM.
Thread Starter
Junior Member
Joined: Mar 2023
Posts: 20
Likes: 2
CL500
The trouble seems to have disappeared but i can't figure what it was. I changed serpentine belt and all the things on it's way. From a sudden few days later, after starting the car it was immediately stalling. I messed around the MAF and other elements like the throttle connector but it was still having hard times to stay at idle.
Attempted many times to restart still same results.
I left it alone decided to search tool to get reading of errors. The day after i started it, it was idling rough, a bit disgusted, i left it warming alone, took a coffee, back to the car it was idling nearly fine.
While driving it, the petrol consumption falled, the car was more responsive, in fact, it was just as it was with bad cylinder before and recovered all it's power. Very very strange.
This is the second day it runs fine. Crossing fingers.
Attempted many times to restart still same results.
I left it alone decided to search tool to get reading of errors. The day after i started it, it was idling rough, a bit disgusted, i left it warming alone, took a coffee, back to the car it was idling nearly fine.
While driving it, the petrol consumption falled, the car was more responsive, in fact, it was just as it was with bad cylinder before and recovered all it's power. Very very strange.
This is the second day it runs fine. Crossing fingers.
