'12 S350 W221 Low Idle RPM
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Junior Member
Joined: Jan 2018
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GL350
'12 S350 W221 Low Idle RPM
I have this annoying issue on my car. Idle runs at 560-580rpms and with a noticeable (diesel) vibration and nobody can figure out why. On this model ('12 S350) it should be 750 rpm. Once in a blue moon, especially when it is cold outside it goes to 750 and runs very smooth for a few minutes but I can't pinpoint what triggers that. Btw, when I say cold, I'm talking about the outside temperature, not the engine ... the engine is warmed up to where it should run. STAR computer scan shows no error codes and looking at live data, parameters are all within range with the exception of idle rpm. All filters changed, DFS is clean, EGR is clean. Injectors checked and run fine. Other than at idle, engine runs great, lots of power and smooth. This has been going on for years now. I even took the car to a Mercedes dealer and they couldn't figure it out either.
Anyone ran into this or has any suggestion of what else could I try?
Anyone ran into this or has any suggestion of what else could I try?
Newbie
Joined: May 2023
Posts: 1
Likes: 0
mercedes s350
I have this annoying issue on my car. Idle runs at 560-580rpms and with a noticeable (diesel) vibration and nobody can figure out why. On this model ('12 S350) it should be 750 rpm. Once in a blue moon, especially when it is cold outside it goes to 750 and runs very smooth for a few minutes but I can't pinpoint what triggers that. Btw, when I say cold, I'm talking about the outside temperature, not the engine ... the engine is warmed up to where it should run. STAR computer scan shows no error codes and looking at live data, parameters are all within range with the exception of idle rpm. All filters changed, DFS is clean, EGR is clean. Injectors checked and run fine. Other than at idle, engine runs great, lots of power and smooth. This has been going on for years now. I even took the car to a Mercedes dealer and they couldn't figure it out either.
Anyone ran into this or has any suggestion of what else could I try?
Anyone ran into this or has any suggestion of what else could I try?
Senior Member
Joined: Jul 2011
Posts: 328
Likes: 56
2012 S350 Bluetec 4MATIC; 2011 ML350; 2005 C230k;
It’s not a problem, this is by design. Increased idle RPM to 750 is only if:
1 - engine is cold so it can heat up faster
2 - DPF regeneration is in progress
3 - battery voltage level is too low
4 - cabin temperature is too high so A/C can run more efficiently
If you have abnormal vibrations, you may check your engine mounts. If the engine is running rough check injectors. But your idle RPM are perfectly fine.
1 - engine is cold so it can heat up faster
2 - DPF regeneration is in progress
3 - battery voltage level is too low
4 - cabin temperature is too high so A/C can run more efficiently
If you have abnormal vibrations, you may check your engine mounts. If the engine is running rough check injectors. But your idle RPM are perfectly fine.
