GLS550 rough idle
05-26-2024, 10:22 PM
#1
Super Member
Thread Starter
Join Date: Oct 2017
Posts: 648
Received 139 Likes
on
106 Posts
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
GLS550 rough idle
In the past week or so my GLS has developed a slight but noticble rough idle. 40k miles…always driven very slowly and carefully…etc. any ideas?
05-27-2024, 09:48 AM
#2
Junior Member
“…slowly and carefully…” could be working against you in this case. I would start with a bottle of BG 44K Fuel System Cleaner. I buy it on Amazon. Your fuel injectors may have an erratic spray pattern from debris or carbon build up which can cause a rough idle.
Run the car until it’s almost out of gas, then dump in a bottle of the BG 44K and fill it up. Drive it until it is almost empty of gas again and then fill normally. I do this about twice a year on my 550.
The other option (much more expensive) is to have your spark plugs replaced.
Don’t use cheap fuel system cleaners as they can damage your catalytic converter.
FCPEuro.com sells a fuel system cleaner from LiquiMoly that is also excellent.
Run the car until it’s almost out of gas, then dump in a bottle of the BG 44K and fill it up. Drive it until it is almost empty of gas again and then fill normally. I do this about twice a year on my 550.
The other option (much more expensive) is to have your spark plugs replaced.
Don’t use cheap fuel system cleaners as they can damage your catalytic converter.
FCPEuro.com sells a fuel system cleaner from LiquiMoly that is also excellent.
05-27-2024, 10:26 AM
#4
Junior Member
Just put it in the gas tank when the car is almost empty and fill it up with gas. Then drive it until it is almost empty again. One tank of gas will do the trick.
05-28-2024, 05:02 PM
#5
Motor mounts? The driver's side mount is really susceptable to failure. When I replaced them, that one was almost completely coming apart and the new one made the car feel smooth as glass again.
05-28-2024, 10:22 PM
#6
Super Member
Thread Starter
Join Date: Oct 2017
Posts: 648
Received 139 Likes
on
106 Posts
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
Does anyone know how to access the MAP on the M278? I'd like to run some aerosolized cleaner through there to hit the intakes and see if that helps, and I need to inject downstream of the MAP.
Trending Topics
05-31-2024, 07:53 PM
#9
MBWorld Fanatic!
Join Date: Aug 2003
Location: In my garage
Posts: 8,528
Received 1,057 Likes
on
849 Posts
E55, GLS450, GL63, GLE350
Sorry, reading comprehension is not always my strong suit. It's often in the heart of the intake so you would probably need to inject at the injector port. There is some risk there that may not be worth the benefit.
05-31-2024, 09:08 PM
#10
Super Member
Thread Starter
Join Date: Oct 2017
Posts: 648
Received 139 Likes
on
106 Posts
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
I just found a pretty decent video detailing the MAS on the M273 - not too complicated to get at. Can't find anything comprehensive for the M278 though.
The following users liked this post:
BlownV8 (06-02-2024)
06-09-2024, 08:17 AM
#14
Out Of Control!!
Join Date: Sep 2018
Location: unbegrenzt
Posts: 13,295
Received 3,916 Likes
on
3,083 Posts
2017 GLE350 4MATIC
It's not the injectors or intake system. It's the ignition or mounting system.
5 year old car = in the realm of replacing both main and aux batteries. If this was my car I would replace both batteries. Modern German cars need 100% perfect electrical systems or they start to misbehave.
Replace the spark plugs and ignition coils. It doesn't matter how many miles you have, or don't have. It's a 5 year old expensive German luxury car. It's how it is. Ignition coils these days are junk consumable parts.
Look in the cam position and cam magnet sensor connectors for signs of oil. M274, M276 and M278 are well known for oil migration from cam position sensors and cam magnets into the wiring harness which creates misfire and rough idle in the early stages, and complete saturation of harness in ECU in later stages.
After doing the above required preventive maintenance, and if there is still a rough idle, look at the engine mounts. They are fluid filled, very soft, and are known to fail. It doesn't matter how many miles you have, or don't have, on the vehicle. These mounts are known to failure earlier than one expects.
5 year old car = in the realm of replacing both main and aux batteries. If this was my car I would replace both batteries. Modern German cars need 100% perfect electrical systems or they start to misbehave.
Replace the spark plugs and ignition coils. It doesn't matter how many miles you have, or don't have. It's a 5 year old expensive German luxury car. It's how it is. Ignition coils these days are junk consumable parts.
Look in the cam position and cam magnet sensor connectors for signs of oil. M274, M276 and M278 are well known for oil migration from cam position sensors and cam magnets into the wiring harness which creates misfire and rough idle in the early stages, and complete saturation of harness in ECU in later stages.
After doing the above required preventive maintenance, and if there is still a rough idle, look at the engine mounts. They are fluid filled, very soft, and are known to fail. It doesn't matter how many miles you have, or don't have, on the vehicle. These mounts are known to failure earlier than one expects.
06-09-2024, 11:35 AM
#15
Super Member
Thread Starter
Join Date: Oct 2017
Posts: 648
Received 139 Likes
on
106 Posts
2015 SL550, 2017 GLS 550, 2010 G550, 1995 E320 Cabriolet
It's not the injectors or intake system. It's the ignition or mounting system.
5 year old car = in the realm of replacing both main and aux batteries. If this was my car I would replace both batteries. Modern German cars need 100% perfect electrical systems or they start to misbehave.
Replace the spark plugs and ignition coils. It doesn't matter how many miles you have, or don't have. It's a 5 year old expensive German luxury car. It's how it is. Ignition coils these days are junk consumable parts.
Look in the cam position and cam magnet sensor connectors for signs of oil. M274, M276 and M278 are well known for oil migration from cam position sensors and cam magnets into the wiring harness which creates misfire and rough idle in the early stages, and complete saturation of harness in ECU in later stages.
After doing the above required preventive maintenance, and if there is still a rough idle, look at the engine mounts. They are fluid filled, very soft, and are known to fail. It doesn't matter how many miles you have, or don't have, on the vehicle. These mounts are known to failure earlier than one expects.
5 year old car = in the realm of replacing both main and aux batteries. If this was my car I would replace both batteries. Modern German cars need 100% perfect electrical systems or they start to misbehave.
Replace the spark plugs and ignition coils. It doesn't matter how many miles you have, or don't have. It's a 5 year old expensive German luxury car. It's how it is. Ignition coils these days are junk consumable parts.
Look in the cam position and cam magnet sensor connectors for signs of oil. M274, M276 and M278 are well known for oil migration from cam position sensors and cam magnets into the wiring harness which creates misfire and rough idle in the early stages, and complete saturation of harness in ECU in later stages.
After doing the above required preventive maintenance, and if there is still a rough idle, look at the engine mounts. They are fluid filled, very soft, and are known to fail. It doesn't matter how many miles you have, or don't have, on the vehicle. These mounts are known to failure earlier than one expects.
The following users liked this post:
chassis (06-09-2024)
