GLS550 rough idle
#1
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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?
#2
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“…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.
#4
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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.
#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.
#6
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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.
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#9
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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.
#10
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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.
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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.
#15
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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.
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chassis (06-09-2024)