bad idle
Thread Starter
Newbie
Joined: Jun 2021
Posts: 7
Likes: 0
2007 s550
bad idle
i have a 2007 s550 with a bad idle when stopped at light or when sitting. ive changed engine and tranny mounts... spark plugs with no change. anybody else have that problem. i had a cadillac with similar symptoms once and turned out to be a leaking intake gasket which smoothed it out. any help would be nice.. 156000 miles
Junior Member
Joined: Dec 2020
Posts: 16
Likes: 6
From: Newport Beach, CA
2011 Range Rover SC Autobiography Black Edition
Hi 1sweat,
Any number of things can cause a rough idle. I understand that you have tried replacing mounts and spark plugs to no avail and that your vehicle has approximately 156,000 miles on the odometer. With this in mind, it may be worthwhile to look into other maintenance items commonly serviced in high mileage vehicles. I believe Mercedes-Benz recommends replacing the fuel filter at 150,000 miles. Beyond that, I would look at the ignition coils, MAF sensor, throttle body, and intake manifold. It can be challenging to diagnose without exacting information and so many things that can be at fault.
As with any diagnostic and repair work, the Mercedes STAR diagnostic tool can be handy with pinpointing issues. If you have access to this diagnostic tool, it may show a fault code despite no warning or error messages displayed on the dash—or the car's computer system may not register an issue with the idle yet.
Keep us posted as you endeavor to solve the problem causing your rough idle.
Best wishes,
Christopher
Any number of things can cause a rough idle. I understand that you have tried replacing mounts and spark plugs to no avail and that your vehicle has approximately 156,000 miles on the odometer. With this in mind, it may be worthwhile to look into other maintenance items commonly serviced in high mileage vehicles. I believe Mercedes-Benz recommends replacing the fuel filter at 150,000 miles. Beyond that, I would look at the ignition coils, MAF sensor, throttle body, and intake manifold. It can be challenging to diagnose without exacting information and so many things that can be at fault.
As with any diagnostic and repair work, the Mercedes STAR diagnostic tool can be handy with pinpointing issues. If you have access to this diagnostic tool, it may show a fault code despite no warning or error messages displayed on the dash—or the car's computer system may not register an issue with the idle yet.
Keep us posted as you endeavor to solve the problem causing your rough idle.
Best wishes,
Christopher
Thread Starter
Newbie
Joined: Jun 2021
Posts: 7
Likes: 0
2007 s550
Hi 1sweat,
Any number of things can cause a rough idle. I understand that you have tried replacing mounts and spark plugs to no avail and that your vehicle has approximately 156,000 miles on the odometer. With this in mind, it may be worthwhile to look into other maintenance items commonly serviced in high mileage vehicles. I believe Mercedes-Benz recommends replacing the fuel filter at 150,000 miles. Beyond that, I would look at the ignition coils, MAF sensor, throttle body, and intake manifold. It can be challenging to diagnose without exacting information and so many things that can be at fault.
As with any diagnostic and repair work, the Mercedes STAR diagnostic tool can be handy with pinpointing issues. If you have access to this diagnostic tool, it may show a fault code despite no warning or error messages displayed on the dash—or the car's computer system may not register an issue with the idle yet.
Keep us posted as you endeavor to solve the problem causing your rough idle.
Best wishes,
Christopher
Any number of things can cause a rough idle. I understand that you have tried replacing mounts and spark plugs to no avail and that your vehicle has approximately 156,000 miles on the odometer. With this in mind, it may be worthwhile to look into other maintenance items commonly serviced in high mileage vehicles. I believe Mercedes-Benz recommends replacing the fuel filter at 150,000 miles. Beyond that, I would look at the ignition coils, MAF sensor, throttle body, and intake manifold. It can be challenging to diagnose without exacting information and so many things that can be at fault.
As with any diagnostic and repair work, the Mercedes STAR diagnostic tool can be handy with pinpointing issues. If you have access to this diagnostic tool, it may show a fault code despite no warning or error messages displayed on the dash—or the car's computer system may not register an issue with the idle yet.
Keep us posted as you endeavor to solve the problem causing your rough idle.
Best wishes,
Christopher
Super Member
Joined: May 2019
Posts: 687
Likes: 293
From: Omaha, NE
2023 S500
My intermittent rough idle turned out to be a broken vacuum line that controls the air injection valves. Different engine, but if the V8 uses hard plastic line for vacuum actuated bits like the V12 does, I'd be checking those.
Thread Starter
Newbie
Joined: Jun 2021
Posts: 7
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2007 s550
Thank you very much I'm going to have my mechanic check that
Super Member
Joined: Aug 2017
Posts: 520
Likes: 203
From: Scottsdale AZ
2015 SL550 & 2012 S550 4matic
Could be bad gasoline carbon buildup..anything in electronic fuel management system.....anything.....don’t replace any more parts without a thorough diagnostic. Mb star is your next step.
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2010 E550, 273 Engine: 2012 S550, 278 Engine
i have a 2007 s550 with a bad idle when stopped at light or when sitting. ive changed engine and tranny mounts... spark plugs with no change. anybody else have that problem. i had a cadillac with similar symptoms once and turned out to be a leaking intake gasket which smoothed it out. any help would be nice.. 156000 miles
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Super Member
Joined: Feb 2009
Posts: 732
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From: Brooklyn, NY
2007 S550 4Matic 2013 S550 Base
i have a 2007 s550 with a bad idle when stopped at light or when sitting. ive changed engine and tranny mounts... spark plugs with no change. anybody else have that problem. i had a cadillac with similar symptoms once and turned out to be a leaking intake gasket which smoothed it out. any help would be nice.. 156000 miles
Thread Starter
Newbie
Joined: Jun 2021
Posts: 7
Likes: 0
2007 s550
Start with a diagnostic before you start replacing parts. I had a bad idle/ misfire and used the Star system to determine which cylinder was the problem and in my case it was cylinder 2. I swapped the coil packs of cylinder 1 and 2 and the problem was now in cylinder 1 which meant that the coil pack was bad. Replacing the coil pack and clearing the error code resulted in smooth idling once again.
