W221 Random Rough Idle and Jerk
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Joined: Jun 2018
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From: Stuart, Fl
2008 S550
W221 Random Rough Idle and Jerk
Hey guys I've got an 08 S550 with 160k miles. The car is extremely well maintained with no check engine lights. It has developed a random problem where the car will stumble at idle and feel like it's going to stall but it doesn't and then a jerk which feels like someone has rear-ended you and sometimes it's pretty severe. Yesterday it was so severe I thought for sure I got rear-ended and I spilled my coffee all over me. I've been searching forums and Google for months now and can't find anything. There was nearly and identical post here years ago but the issue was never resolved. I PM'd the original poster and got no reply. I plan on checking air box fitment air filters spark plugs vac leaks coils and lastly the throttle body. Any help would be greatly appreciated.
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From: Stuart, Fl
2008 S550
Thanks for the tips and I will look into it I only have a basic code reader and there are no codes on the car whatsoever and as a matter fact I have never had a single code in the five years I've owned it. I have to confess I run 87 octane in the 5 years I've owned it with zero issues but just to eliminate the possibility I'm going to run the gas down and fill it with premium just on principle.
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From: Miami, FL
2003 CL 600
Check the pcv lines around the throttle body. Without proper diagnostics, throwing parts at it won't help.
You should be using premium fuel anyway but that won't cause the issue you're having, nor will changing one tank make a difference now.
You should be using premium fuel anyway but that won't cause the issue you're having, nor will changing one tank make a difference now.
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From: Stuart, Fl
2008 S550
Well spent the weekend looking for vacuum leaks visually and using starting fluid and everything seems tight no leaks. I did however replace the dipstick o-ring as it was actually missing! Car still has the random problem. I agree with an earlier post, I don't want to just start randomly replacing parts but I still feel like there's got to be something I'm missing that's obvious. The car still has yet to throw any codes. And again I realize it's probably irrelevant but I'm waiting to run this tank of gas down to fill up with premium just on principle.
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From: Stuart, Fl
2008 S550
Unfortunately I do not have access to that I've considered purchasing it but from what I've read There is a m learning curve just to learn how to use the software and I'm more of a wrench head than a software person. I have a vintage Ferrari that I work on with my eyes closed.... this Mercedes crap is for the birds. I just had to pay 400 bucks to have my AC recharged because I replaced the radiator and discharged the system. The car would not let me recharge it... it's ridiculous.
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Thread Starter
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From: Stuart, Fl
2008 S550
Well I am pleasantly stunned the problem seems to have gone away! 3 days and counting. Really all I did was replace spark plugs air filters and that dipstick o-ring. But the air filters were extremely dirty and dusty.
The only thing I can think of is that the engine has sort of adapted itself with the new clean air filters either via fuel mixture, mass air flow sensor, O2 sensors or whatever. All know is it's running perfect at the moment and I'll take it. Will keep you posted.
The only thing I can think of is that the engine has sort of adapted itself with the new clean air filters either via fuel mixture, mass air flow sensor, O2 sensors or whatever. All know is it's running perfect at the moment and I'll take it. Will keep you posted.
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From: Miami, FL
2003 CL 600
It may have been because of the crankcase leak from the dipstick o-ring. The cars do funny things when the system isn't sealed.
If your TB is dirty, it will have issues trying to adjust further closed than normal to sustain idle with an air leak, but once you fix the leak it should go back to the correct position and manage.
If your TB is dirty, it will have issues trying to adjust further closed than normal to sustain idle with an air leak, but once you fix the leak it should go back to the correct position and manage.
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From: Stuart, Fl
2008 S550
Thank you for the reply. As dirty as the air filters were the throttle body was actually spotless. They were OEM filters that I have not changed in a couple of years and I have been driving in some really dirty conditions like dirt roads Etc. I drove the car a lot today and it was extremely hot down here in Florida 92 on average and it drove perfectly. I also had put a new radiator in it so it is cooling quite well.
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S550 w221
My s550 has the same exact problem! HELP
Hey guys I've got an 08 S550 with 160k miles. The car is extremely well maintained with no check engine lights. It has developed a random problem where the car will stumble at idle and feel like it's going to stall but it doesn't and then a jerk which feels like someone has rear-ended you and sometimes it's pretty severe. Yesterday it was so severe I thought for sure I got rear-ended and I spilled my coffee all over me. I've been searching forums and Google for months now and can't find anything. There was nearly and identical post here years ago but the issue was never resolved. I PM'd the original poster and got no reply. I plan on checking air box fitment air filters spark plugs vac leaks coils and lastly the throttle body. Any help would be greatly appreciated.
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Joined: Aug 2014
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S500
CPS (crank position sensor) - easy-ish home job $50 - is a normal modern car issue. They tend to go to 10 years 50k before they play up - progressively get worse till they won't start when hot
Coil pack(you have 8), again 10 years 50k miles normal life, 5 of mine have died (damages the CAT) . Should always have one spare in the boot/trunk on these cars....
both should show up it as a fault on a diagnostic scan
Coil pack(you have 8), again 10 years 50k miles normal life, 5 of mine have died (damages the CAT) . Should always have one spare in the boot/trunk on these cars....
both should show up it as a fault on a diagnostic scan
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S500
reading the first post more thoroughly..
if its not the normal stuff in my post above, it might be the auto-box TC clutch. These can be worn out and trying to lock the Torque converter up 1 to 1 when it needs 100% slip at idle. This is also a common failure mode on Mercedes and is expensive, as the box has to come out and the torque converter gets replaced
it can be turned off using STAR and if the fault goes away you know what's driving it
if its not the normal stuff in my post above, it might be the auto-box TC clutch. These can be worn out and trying to lock the Torque converter up 1 to 1 when it needs 100% slip at idle. This is also a common failure mode on Mercedes and is expensive, as the box has to come out and the torque converter gets replaced
it can be turned off using STAR and if the fault goes away you know what's driving it
Last edited by BOTUS; Dec 7, 2021 at 12:33 PM.
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From: Stuart, Fl
2008 S550
I finally did fix the problem once and for all 100%. Turns out the throttle body was dirty but it took a mirror and a light to actually see what was going on. There was literally puddled oil at the bottom of the throttle body ... it was so much oil I could literally hear it gurgling as it was trying to suck air. Was an easy fix just a nice rag and some carb cleaner and I manipulated the throttle body butterfly and wiped it out really really well. To get to it you have to remove your airbox your mass air flow sensor and then the large plastic elbow which snaps in place... it's quite easy. Do it with the engine cold cause the throttle body gets very very hot! In case you're wondering where the oil came from there is a crank case vent at the rear passenger valve cover that literally dumps oily vapor right into the throttle body for pollution control. It's no wonder there was oil built up after 11 years of output. Guarantee this is your problem.
Last edited by Polo35m; Dec 7, 2021 at 12:53 PM.
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S550 w221
I will check it as soon as possible!
I finally did fix the problem once and for all 100%. Turns out the throttle body was dirty but it took a mirror and a light to actually see what was going on. There was literally puddled oil at the bottom of the throttle body ... it was so much oil I could literally hear it gurgling as it was trying to suck air. Was an easy fix just a nice rag and some carb cleaner and I manipulated the throttle body butterfly and wiped it out really really well. To get to it you have to remove your airbox your mass air flow sensor and then the large plastic elbow which snaps in place... it's quite easy. Do it with the engine cold cause the throttle body gets very very hot! In case you're wondering where the oil came from there is a crank case vent at the rear passenger valve cover that literally dumps oily vapor right into the throttle body for pollution control. It's no wonder there was oil built up after 11 years of output. Guarantee this is your problem.
Thread Starter
Member
Joined: Jun 2018
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From: Stuart, Fl
2008 S550
Not at all on a scale of 1 to 10 it is about a 2 or 3 on difficulty level. Do it with your engine cold and it's very simple... you remove the air filter housing, then you remove the mass air sensor, then the 90deg plastic elbow. Then set up a drop light and your wife's makeup mirror and look at the throttle body. In my case there was liquid oil puddled at the bottom. Was as simple as wiping it away! You can push the butterfly flap and clean as well.
