W124 rough idle

W124 rough idle

This article specifically covers the W Mercedes with the M engine, however the concepts I'll go over apply to nearly all fuel-injected gasoline engines. In a gasoline engine, the speed of the engine is controlled by the amount of air that enters through the throttle body. In a diesel engine, there is no throttle body.

The speed of the engine is controlled by the amount of fuel injected into the cylinders. Diesel engines are a different animal that we will cover in a different article. A poorly running car can often run amazingly well after an afternoon's worth of work, going through the various rubber boots and hoses around the engine. Vacuum lines, intake boots, seals and many other small gaskets around the engine can be the source of poor running and idle problems.

Many times, a lean running condition can be traced back to a cracked or torn boot in the system. A good quick way to check the overall health of the system is to take the oil filler cap off with the engine running. If the system is in good shape, the idle of the engine should drop and the car will run rougher. This is due to the extra unmetered air flowing through the oil filler port.

If there is no change in the vehicle's idle, then you probably have a vacuum leak somewhere in the system. Don't forget to check places where vacuum leaks may not be as obvious, such as the oil filler cap, the dipstick and also the valve cover. The cover itself has 23 different seals on it! Each fastening bolt of the cover uses a sealing grommet underneath it. These are especially susceptible to cracking as they age. Replacement is pretty straightforward: just loosen each 10mm bolt, then pry the old sealing ring out of the valve cover and replace it with a new one.

Around the perimeter of the valve cover, you'll want to replace the cover gasket as well as the 6 grommets that get sandwiched between the cylinder head and the valve cover. Both the valve cover gasket and spark plug grommets need to be glued into place.

This is most easily done by using a few dabs of gasket adhesive every couple of inches in the channels around the perimeter of the valve cover and also the spark plug holes. One problem with the M is that corrosion develops under the coating on both the inside and outside of the valve cover. The coating on the valve cover is something similar to powder coating.

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I've been told that this coating was added to aid in sound deadening on the top of the engine. I haven't been able to find any information confirming this, but it seems consistent with the engineering of the car.More often that not a customer just wants to know what part to buy to fix the problem. If your older gas engine, starts hard, idles poorly, or accelerates with hesitation the problem may or may not be solved with replacing a part or parts.

rough idle

The problem needs to be approached first with a thorough understand of how to troubleshoot the cause or causes BEFORE you throw parts at the problem. For instance you don't want to order a new fuel pump just because your engine is hard starting. My merc is a manual, petrol W E from and has KM, in very good condition no rust, almost full history etc I really enjoy driving it around and wouldn't trade it for any recent model.

However something has been bothering me ever since I acquired it. I'm very attached to this car and have already brought it to a Mercedes repair shop and they haven't been able to identify the problem, all they could do is stress that the car has no problem when driven no power loss, no jolts, no abnormally high fuel consumption or anything of the sort. They have tested and ruled out the following: - Spark plugs - Fuel pressure - Intake manifold sealing - Air mass sensor I know from the history that the fuel pump was changed not long ago before I brought the car, but the Mercedes guys found nothing wrong with it.

And here's also something that may or may not be relevant: the bouncy idle happens only when the car is fully stopped, ie as long as the car is advancing even slowly in neutral gear, the rpm is perfectly stable, but as soon as the car stops, it starts bouncing like in the video Have you already seen this situation? Is there anything I can do about it? Thanks a lot, Lucas P. Hi Lucas, Your problem is not uncommon especially as these cars age. Sometimes it is not so easy to find the real culprit.

Should not be so on your engine.

w124 rough idle

I would start by doing a compression test on the engine. If your compression is not equal that will cause the rough idle. Once you know your compression is good. Spark next: you said you replaced the spark plugs but nothing about the wires or the distributor cap.Or maybe you hear a skipping sound when the engine is running.

rough idle

All these are symptoms of a rough idle. Incidentally, the mechanics at JL Motorworks are experts at quickly diagnosing the root cause of your rough idle. Call to schedule an appointment today! As with many car issues, the root cause of a rough idle can either be a quick, easy, inexpensive fix, or it can be something more serious and costly. The idle speed of an engine is the rotational speed of the engine when it is not connected with the drivetrain and the throttle gas pedal is not being depressed.

According to Mister Transmission :. The drivetrain includes the transmission, the driveshaft, the axles, and the wheels. Simply put, it works in conjunction with the engine to move the wheels. The drivetrain system is an essential component of a vehicle and the transmission is an integral part of the drivetrain. When an engine is running at idle speed, it generates enough power to operate systems such as the water pump, alternator, and power steering — but not enough power to move the vehicle itself.

A passenger car will usually idle between RPMs.

Top 10 Causes of a Rough Idle

A properly functioning idle should feel smooth — no bumps or skips. Express Auto Inspections says:. While modern vehicles use a fuel injector system to burn gas, many older cars use a carburetor to process fuel.

As your car rolls along, the engine takes in a mix of air and fuel that allows it to keep moving. This intake relies on a vacuum that is created between the carburetor and the piston tops… If there is a leak in this vacuum, the ability for your car to gain energy from the burning fuel is compromised, causing rough idling. Fuel filters screen contaminants out of the fuel before it goes into the engine.

No need! Fuel injectors inject fuel into the cylinders to create a mix of air and fuel to burn.

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They need periodic TLC to keep gunk from building up. A rough idle could simply be the result of an incorrect idle speed setting.

A trained mechanic can reset your idle speed setting easily. Spark plugs create the spark that is needed for your car to burn fuel. Damage to spark plugs or spark plug wires can cause a rough idle, as your engine is struggling to process the fuel it needs to run smoothly.

This can cause the car to have higher revolutions per minute, shake while idling, produce a high-pitched squealing noise and even begin to stall or backfire. It is a computer that controls the ignition coil and regulates spark generation in the engine. The fuel pump pulls fuel from the gas tank to the fuel injectors.

Over time it can become clogged, resulting in a rough idle, sputtering, stalling, and slow acceleration, as the engine is unable to get enough fuel. Oxygen sensors measure how rich or lean the gasses are as they exit the combustion chamber.

A dirty oxygen sensor will usually trigger the check engine light and can lead to a rough idle, lower fuel efficiency, and a failed emissions test. Some older cars use a carburetor to process fuel, rather than a fuel injection system. No Comments. Does your vehicle seem to be roughing it lately? What is Idle Speed? According to Mister Transmission : The drivetrain includes the transmission, the driveshaft, the axles, and the wheels.The clack would also disappear during the summer and return when cooler weather returned.

Most of that quarter inch drop could have taken place right after radiator work and be due to air working its way out. Yes it does disappear after yards. It was the same scenario you described: cold start and then accelerate up the driveway going up a moderate rise. In regards to that coolant leak. The coolant puddle is below that pipe, however the cylinder head surface around the pipe seems to be dry.

The hose which is connected to the pipe is dry too. The first 2 pictures shoe the coolant leak area. But you certainly know how to interpret them better than me. I had to use a very small camera due to space limitation and hold it next to the oil filter the blue thing on the left of the picture.

That way I could take the picture from the bottom up. On the cylinder head surface below the hose there are some traces of reddish stuff and some dark traces which seem to stem from running liquid. After I took the picture, I cleaned that wet spot on the block and drove about 10 miles. After that everything was still dry. I checked again an hour later: still dry the coolant hose was still warm. I checked again seven hours later: the wet spot was back!

Then I checked the surface of the cylinder head below the pipe with my finger: wet! The end and the underside of the hose were dry. The pipe is tack-welded to a bracket which is flanged onto the side of the head. HD, you have mentioned before the possibility that your timing chain could be stretched slightly. Be prepared. Make sure you have a new one on hand. Yes, I am also enjoying this thread.

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I also appreciate that H. There are a number of German forums on the web dealing with this idle problem on the M, M and M engine. Some people say they solved it by fixing false air leaks, some by renewing things like the distributor, the injectors, the OVP relay, the air flow sensor potentiometerthe EHA, and several other things. One guy said, that he fixed it by renewing the heat sink paste between the ignition ECU and the surface it is mounted on. Some people in these forums talk about expensive and unsuccessful attempts at Mercedes workshops to solve this problem.

But most of these discussions just stop at some point without a solution - at least without the announcement of a solution.

w124 rough idle

Besides idle the engine runs very smoothly not only during acceleration, but also during cruising at any rpm range. With the chain travelling clockwise it is rail-guided 3 on the tractive side over almost the whole distance between both sprockets.James answered 7 years ago.

Robert answered 7 years ago. I'm positive it is not a clogged cat. I believe it's a major Vacuum leak. Hopefully your leak is easier to find.

David answered 7 years ago. I checked the brake booster a few months agoand wasnt that, i will have to get a cigar tomorrow and smoke the engine see if i can find a leak. You're talking the cold start injector? Very possible, though it could just as likely be that injectro is leaking as the sensor acting up. The injector is right there towards the front of the engine if you're wanting to pull it out and see if it's leaking or still spraying when the engine is hot.

Stefan answered 7 years ago. I will check it out, I was actually referring to the cold temp sensor, if its saying its 30 below zero then it will dump fuel into the system, but the thing that gets me is that in idle its pretty much normalonly acts up in gear. MercedesMonkey answered 4 years ago. Sitting on the side of the road in my SEL waiting for AAA, I've had almost everything replaced to fix this problem, literally 10k into this 4k car And no one mentioned a vacuum leak Could be the Bosch EHA valve.

It can be worn out and become temperature sensitive to functioning, working well when engine is cold, but irratic when warm. The cool gas going into it complicates the picture because once you stop the car the gas warms up in the area and makes starting difficult until cool gas reaches it again, but it may not be cool enough anymore with a hot engine under it.

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New, these are very expensive little critters. Guru6S3CF answered 3 weeks ago. No, I found a brick of coke stuffed in one of the exhaust pipes.

I bought the car in 86, so sign of the times I guess.

w124 rough idle

It's been in there for 35 years! Can anyone please let me know where I could possibly find the side trim panel grey for a white mercedes E Had a rear tire blow-out on the motor way today, and it broke the grey panel betwe I have some experience working on cars Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus.

Please refer to CarGurus Terms of Use. Content will be removed if CarGurus becomes aware that it violates our policies. Report Follow. Mark helpful. Your Answer:. Upload Photo Photo optional. Related Questions. Start a new Mercedes-Benz Class question.Log in or Sign up. Mercedes-Benz Owners' Forums. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies.

Learn More. Messages: 46 Likes Received: 0 Joined: Dec 22, Hi Guys need some advice! While driving yesterday enjoying the weather I was parked at some traffic lights, When all of a sudden the engine began to idle rough and lumpy and when I accelerated from the lights the lumps in the idle seem to get worse. I parked up restarted the car and the problem was still there and still is.

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When I start the car its sounds rough and juddering and when I rev the gas up it judders and even more. This is really bugging me!! I am so gutted!! WConvertibleMay 25, Messages: 7 Likes Received: 0 Joined: May 24, Hi, could be a few different things but sounds like a crankshaft position sensor or knock sensor, you could guess and replace one at a time but to be sure i would definately get it put onto a diagnostic tool.

Could well be the fuel pump on the way out. Or possibly a clogged fuel filter. Does it ever stall completely?

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Because the fault is so obvious, it is likely that 2 cylinders are down, so a coil has probably blown. When you get to the coils under the top cover, you could take a lead off one of the coils, ignition off. If no effect, that is the problem coil, If worse that is a good coil - you get the picture.Forums New posts Search forums. Members Current visitors.

Log in Register. Search titles only. Search Advanced search…. New posts. Search forums. Everywhere Threads This forum This thread. Log in. Contact us. Close Menu. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Home Forums Technical Engine. W Rough Idle. Thread starter Bean Start date Sep 22, Tags idle rough w Bean Member. I have what seems to be a common problem with this car - rough idle.

The car is a W E estate. M engine. The car idles between and and after 5 minutes it stalls. I noticed in the service history that in the car had idle problems and the MAF was replaced with a used one which seemed to fix it — until now.

The loom was also replaced about 10 years ago. There is the smell of petrol so there might be a problematic charcoal filter. The closest specialist is a 2 hour drive away. Any help or advice would be much appreciated. Joined Sep 28, Messages Location south east Car '93 te. The valve is only activated under certain conditions, above a certain coolant temp etc. Full details here Have you tried running the engine with MAF disconnected?

If so did it run worse or the same? Same deal with the purge valve but you obviously need to block the hose that goes to the engine or you'll have an air leak into the inlet manifold Does the car have cruise control?

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