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Mercedes S212 – M271 EVO (Turbo) – Rough idle in D after coolant radiator replacement
Hi everyone,
I have a Mercedes S212 with the M271 EVO turbo engine. I recently had to replace the coolant radiator. On this model, the transmission oil also flows through the radiator.
At first, I thought I didn’t need to top up the transmission fluid because only a small amount passes through the radiator. After driving the car, I checked the level and it was slightly below halfway. I added about 100 ml of genuine Mercedes ATF, but the issue is still there.
Now the problem:
When the car is in Drive (D), idle speed is 657 rpm and the car has a noticeable vibration / rough idle (feels like it’s underloaded). (Photo attached)
When in Park (P) or Neutral (N), idle is about 752 rpm and smooth. (Photo attached)
The gearbox shifts perfectly, there are no unusual noises, and the ATF level is correct.
01. Did you test tranny oil level with engine running and what tranny oil temperature you are getting ?
02. Do you know that the 5 speed transmission tranny oil temperature can only be read while in D and not while in Neutral ?
If in N, you get COOLANT TEMP, but in Tranny Oil Temp data field , cheapo Mercedes design on its electronics, trying to save bandwith or what ?
Below is actually D mode and not N, the data reporting is slow this tranny and I took photo too fast. The 55C is indeed the tranny oil temperature.
Below is true in Neutral. Thus you see coolant temp at tranny oil temp data field... aftermarket scanner may fool you, if the data explanation "i" symbol is not included like in Xentry.
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03. If in D and RPM rise to say 1,000 to 1,100 RPM, is the vibration still there ?
04. Did you check the misfire count, your scanner can do that right ?
Tip: This thing still persist untill this day. It's a normal thing, documented in a GF document for 5 speed gearboxes. (also for trucks ) it's a common thing for mercedes/daimler.
So yes, i tested in Drive, 80C trans temp, the level is correct.
03. If in D and RPM rise to say 1,000 to 1,100 RPM, is the vibration still there ?
No, the vibration dissapear. The vibration is only because the engine is at 650rpm. (low idle)
04. Did you check the misfire count, your scanner can do that right ?
Ok, 90% chance it is your engine mounts then. And tranny mount too while at it.
Also I think your engine can not do idle in gear in D at 650 RPM, it is too low.
There is a setting equal to oldie car Idle-up when HVAC is turned on.
Here is my friend's C200, same engine as yours, this is in D brake hold, before I told him to do WOT 1 , 2 and 3rd gear.
See the idle speed info in green.
Below is 1st gear nearing WOT RPM. See the ECM setting for RPM at idle now down from 750 to 650 RPM.
2nd gear heading WOT RPM
Try to calibrate the idling speed too, the thottle body.
Aside from checking you engine mounts.
.
If your engine mount rubber flap already kiss its lower base like below photo , that is a goner engine mount.
This is the same C200 , M271.8 engine on the Xentry example.
The vibration effects can be seen on the engine mount. Aside from the vibration sensed by our azz-dyno
I checked all the engine/trans mounts. They are in perfect condition.
See my screenshots from the diag, i have 650 in Drive With AC on..., and with AC off, still 650. (Standstill, with brake applied)
I did a throttle calibration, no difference.
LE: Idle recognition is on at 650rpm when in D and brake applied.
In that case inspect your induction system. What were removed during radiator change process, trace back.
Look for induction / vacuum leak.
Inspect the EVAP system, the L rubber hose often crack at 10th year and up.
Your turbo boost solenoid on M271.8 is not using vacuum pump, it is using induction system vacuum and pressure, so inspect that too as part of vacuum leak.
The 110/3 and 110/5 cooled air intake hoses has o-ring, see if the o-rings are good.
Smoke test will be good.
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Can your scanner see the data pid 238 of Xentry , the INCREASE OF SPECIFIED IDLE SPEED ? and the 147 IDLE RECOGNITION ?
What is your engine B28/7 intake pressure sensor ( intake manifold ) value at idle in N ( 750 RPM ) and in D ( 650 RPM ) hot engine ?
Also what is the fuel pressure at FUEL RAIL and the Low Pressure fuel filter pressure at N ( 750 RPM ) and in D ( 650 RPM ) hot engine ?
See below a normal parameter of my friend's M271.8, for you to compare with. Its in NEUTRAL, hot engine.
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Attached M271.8 EVO engine booklet, if you don't have it yet.
1) No secondary air injection.
2) No hoses/pipes are broken.
3) I don’t have idle recognition
4) the values are almost the same as your example.
attached you will find 2 screenshots, one is with N, and other one is in Drive with brake. (The one with 650rpm)
1) No secondary air injection.
2) No hoses/pipes are broken.
3) I don’t have idle recognition
4) the values are almost the same as your example.
attached you will find 2 screenshots, one is with N, and other one is in Drive with brake. (The one with 650rpm)
You mean your scanner does not have the : INCREASE OF SPECIFIED IDLE SPEED "XX" RPM information.
Try to find this data PID.
By logic the ECM if commanded 750 RPM for idle, engine will have to idle at 750 RPM gear engaged.
1.8 Liter engine is small, S212 is heavier than W204 C200 by 300kg at least.
It is normal for small engine to not have enough torque at low RPM, hence the idle speed can not be too low when gear engaged in D.
My 1.8L Toyota Corolla Cross with CVT tranny, its idle in gear is also 750ish there about.
My E400 can idle in gear D2, brake hold as low as 535 RPM, but it has the torque.
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I think you must first sort out the matching RPM for INCREASE OF SPECIFIED IDLE SPEED "XX" RPM to achieve its target.
Because as you stated, at 750 RPM in D, no more vibration.
Second suggestion, just as precaution if tranny is the cause of the higher engine load
When you replaced the radiator, where was the leak ?
Since it is shared tranny oil and engine coolant radiator, often I see the tranny oil cooler section of the radiator is the one leaking first, and tranny oil get contaminated by coolant.
Since 5G tranny oil filling procedure to proper level is easier than 7G, perhaps try to drain the tranny oil and see if you got any coolant trace ?
I managed to get access to the “specified idle speed” values and I noticed the following:
In N, I have 750 requested, and 750 actual value, without vibrations, everything ok.
In D, with the brake pressed, I have 650 requested, and 650 actual value, but it feels like the car is shaking, because 650 is a much too low rpm.
I did notice something interesting in the TCM though: (I also attached pictures)
Status of torque converter lookup clutch is OPEN whether I am in P or in D (brake pressed)
In P the rpm difference is 36rpm
In D (brake pressed), the rpm difference is…662rpm.
Now maybe I don’t understand very well how this lookup clutch works. But shouldn’t it also be “closed” at some point? I tried driving the car and it doesn’t change.
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1) the old radiator was losing antifreeze due to its age, out of curiosity I tested the oil radiator from the inside and it had no leaks. - guaranteed I don't have antifreeze in the oil and vice versa.
2) I tested each hose, both visually and by spraying brake spray on each joint, the car doesn't react, so it's not pulling "false air" somewhere.
Well, the fuel pressure looks like S-Prihadi known good car…I think that it’s normal to see a difference between 750rpm and 650 in terms of rail pressure. No?
if not, where i can start checking if it’s something wrong with rail pressure ?
update: the status of torque converter lookup clutch works, it’s slipping/open to slipping when I’m driving.
so, ignore my last reply about this.
but i still suspect the trans…even if it’s shifting and doing it’s job flawless after 330.000km…
1 bar equals 14.5 psi and you have roughly 4 bar difference at the fuel rail, that's about 60 lbs difference. I think (not educated in Mercedes fuel pressures) that there wouldn't be nearly that much difference. If it hadn't been mentioned by someone else, I might not have even thought about it.
Thank you. What you say makes sense, it's a big difference.
But look, the pressure requested is identical to the pressure provided. so unless the car is requesting something wrong. And here I'm a bit doubtful. I think the pressure value is a sum, including the feedback from the speed sensor (which automatically decreases) and many others. Looks like a dead end to me.
One screenshot is in N, the other in D.
*somethimes the idle stays at 700in D.(even the requested value is 700)
M271 EVO high pressure injection system is like that, kinda variable pressure at low RPM, it is old style HPFP, only 140 bar max.
Don't worry about it.
It does not behave like M276.x HPFP which will maintain minimum 100-120ish BAR at idle and can peak to 200 BAR, but will do 120BAR at higher RPM when you are throttle heavy.
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Something else to try and confirm :
01. When you are in D, but do not brake and do not add throttle, let the car roll on its own on a flat road....what is the RPM you are getting ? and is the shakey2 still there ?
If 01 is smooth while car rolling on its own in D..... do 2nd test.
02. Apply parking brake maximum click. Engage D and let go of the normal brake, rely on parking brake to stop the car. .What is the RPM you are getting ? and is the shakey2 still there ?
I am looking for brake booster internal leak causing vacuum leak to your engine.
NOTE : I have not personally studied the M271 EVO brake booster vacuum source.
Some engine uses vacuum pump and engine intake manifold (with check valve ) at the same time to provide vacuum for brake booster, example M157 andM278.
M276.8 3.0 TT, brake booster is supplied only by vacuum pump.
M276.9 3.5 NA, I don't know.
There is no WIS on where the vacuum hoses true routing are.
So we must visual inspect it one by one and draw our own diagram
I got a little angry with the car (I feel like throwing it off the bridge) and drove a little more aggressively with it. (kickdown acceleration from 0 to 185)
After all that work, I pulled over, and in D I now have requested engine speed 750, and constant speed 750 in D.
now, I don't know, maybe he likes the aggressive style...I'll look for a GF document in wis about that )
All in all, if the problem reoccurs, I'll do what you recommended with the "HOLD" brake and see.
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but I'm thinking about one thing. namely that the only place I went to vacuum was at radiator shutters, where I removed the small hose that went into the valve on the radiator. and my logic is like this.
in P radiator shutters are closed. when I put in D the radiator shutters open, and vacuum is lost there…
Aha....yes, this engine is part of the blue efficiency bull-shi-et and even in tropical country they have the ***** to install the radiator shutter , my friend C200 has the radiator shutter.
So it is vacuum pump powered , I re-read the M271 EVO engine document I posted.
So there is Tee connection somewhere at the vacuum pump to brake booster routing, for the radiator shutter.
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Italian tune up is always good to maximize engine full operation.
Once in a while do 6,500 max RPM 1st and 2nd gear, that is still within speed limit of your country I am sure.
For my engine and my country "loose" speed limit, for me 3rd gear WOT is do-able if traffic is loose at paid highway.
Hope your engine stay good and well behaved.
330,000KM is a lot, it will equal to 100,000KM approx in terms of engine torture if driven in Jakarta bad traffic where average speed is 21KM/H at best,
for mix paid highway and regular road use or approx 4,750 hours engine running.
Well, I wanted to go by car…and a wild icon appeared on the dashboard ))
I took the alternator off and the carbon brushes were...missing )
I replaced the carbon brushes (an easy procedure) and everything is ok now.
It's worth mentioning that it was the original regulator plate, from 2011 with 331k km. so it lasted quite a while.
I was happy because I thought that was where the problem with the low engine speed came from.
however... the rpm is still at 650. I also tried the parking brake thing (to eliminate the vacuum problem) but still the same.
I'll give it a little boost tonight and see if it does the same as today. (it should stay at 750 after a more hectic ride)
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, cheapo Mercedes design on its electronics, trying to save bandwith or what ?
) it's a common thing for mercedes/daimler.
With AC on..., and with AC off, still 650. (Standstill, with brake applied)
