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Discussion Starter #1
I have a 1997 S420 with 161,000 miles on it and I just went out today to drive it and after about 1/2 hour of driving it began idling very rough and hasn't stopped. I popped the hood and the engine visibly shakes and the CEL is on.

What's interesting is that it idles rougher at a stop, is sluggish from about 1000 to 2500 rpms and seems smooth after 2500rpms and has no rouh idle when stopping. I also noticed a sulphur smell.

I put some fuel treatment in thinking it might be some gunk in the fuel injectors and I revved it up to 5000rpm and drove it for a while but no change!

I've read a lot of threads on here about this problem and I've seen everything from cylinder misfires, coil changes, and wiring harness problems but I can't seem to decipher anyone who has had all of these "sypmtoms" with their car.

Any help would be greatly appreciated!

benzgirl13
 

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Administratoris Emeritus
2021 SL770
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46,428 Posts
Welcome to BenzWorld benzgirl13! I'm going to move your query over to the w140 section, where you're more likely to garner a helpful response.
 

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2003 Mercedes Benz E500
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668 Posts
Hopefully...

you revved the car to 5K RPMs while in motion...

Okay, your car is most likely too late in the production run for the wiring harness problem. The most likely suspects are coil pack(s) or a bad MAF [air mass sensor].

The most likely reason that you feel the miss more at idle is engine mounts; if the mounts are marginal, or worse, more vibration is transmitted to the chassis.

You can take your car to AutoZone, and they will pull the OBD codes for free. Post the codes here [the actual codes and not the counterman's interpretation] and someone will most likely chime in with a diagnosis.

Good luck,

JR
 

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Discussion Starter #4
you revved the car to 5K RPMs while in motion...

Okay, your car is most likely too late in the production run for the wiring harness problem. The most likely suspects are coil pack(s) or a bad MAF [air mass sensor].

The most likely reason that you feel the miss more at idle is engine mounts; if the mounts are marginal, or worse, more vibration is transmitted to the chassis.

You can take your car to AutoZone, and they will pull the OBD codes for free. Post the codes here [the actual codes and not the counterman's interpretation] and someone will most likely chime in with a diagnosis.

Good luck,

JR
Thank you, E Class Owner.

I went out to Auto Zone and they diagnosed it as P0309, cylinder 2 misfire. I do remember that I read a thread that had a cylinder 7 misfire and it turned out he had to replace multiple coils before the problem was resolved. I am imagining that might be what I have to do.

Does anyone have any suggestions?
 

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1989 190e 2.6 1993 500sel (sold) 1995 S500 coupe (sold) 1994 S500 blk/blk
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It's the 80/20 rule. Of the 80% of cars on the road, 20% of them develop a sudden performance problem and of that twenty percent, 10% will need to be towed to a shop for repair or the junkyard.

Your problem could be caused by any number of faults, but I suggest that you start with a simple visual inspection for cracks and leaks in your vacuum hoses. But it seems to me based on the symptom that you describe (the sulpher smell) that your oxygen sensor is shot and needs to be replaced, and worst case scenario your catalytic converter could also be shot, needing to be replaced.

Could be any number of faults and/or a combination of them, but start and think about the simple possible causes.

Good luck!
 

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1997 S420, 2000 E320
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Yes, it is a bad coil. You can get them online for around $70. You will need to change the one on cylinder 2. It is a pretty easy change. There are lots of posts on here about how to do it. Good luck
 

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2003 Mercedes Benz E500
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668 Posts
If you change...

the coil pack, pay attention to the condition of the "boot connector" that goes in between the spark plug and the coil pack. If it looks like the contacts are "burnt" then replace this piece as well; if you are unsure, then just replace it for good measure, as the piece only runs about $8.00.

These engines are known for eventually having coil packs fail. My local Mercedes dealer has a practice that if two or more are bad, they replace them all.... ouch! [This is one reason why I avoid the dealer...]

Good luck on the DIY repair.

JR
 
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