Hi everyone,

I recently ran into an issue with my car and I’d appreciate any advice you can give. The car started shaking slightly while idling, and shortly after, the yellow check engine light came on. I ran a diagnostic scan, and these are the codes I got:

• P031: Misfire detected on cylinder 1
• 0521: Irregularity in the intake flap operation for cylinder 1
• 0629: Combustion failure
• 0633: Combustion failure in cylinder 1

Given these codes, I’m not sure where to begin with the troubleshooting. Does anyone have experience with similar issues? Here are a few thoughts I had but would like confirmation or other ideas:

1. Spark Plug/Coil Issue: Could this be as simple as a bad spark plug or ignition coil for cylinder 1?
2. Intake Flap Issue: Should I inspect the intake flap or actuator for cylinder 1? Could carbon buildup or a mechanical failure be causing this?
3. Injector/Combustion Issue: Could it be related to the fuel injector? Should I test the injector for cylinder 1?
4. Other Suggestions: Could something else li
   
   
   ke a vacuum leak, wiring issue, or ECU problem be involved?

I’d love to hear any ideas on where to start my inspection or if there’s a sequence you’d recommend for narrowing this down. Thanks in advance for your help!

What engine do you have and what year?

From my quick searching around i would inspect the front of the air intake and look at the levers that operate the flaps, see if any are broken or popped off. Shown in the red square below:






For the misfires you may want to check fuel injector 1.

The root cause appears to be your intake plenum flap disturbing airflow.
Address this first.

Is a M272 in w204 year 2007

I would follow Tim’s advice to start. Visually inspect and make sure the rods are connected and not snapped. It’s not an uncommon problem at all on these engines.

Next, I would change all the plugs and coils and run a tank of fuel cleaner. I actually just changed all of mine with OE parts bought off rockauto, they’re having a sale and I got it all for $200 shipped. OE means it’s the exact same part and manufacturer you get from Mercedes, but without the badge.

For fuel cleaner, either do Chevron Techron or Liqui Moly jectron cleaner.

Here’s a link to my thread with part numbers and everything: https://mbworld.org/forums/c-class-w204/905642-spark-plug-coil-advice.html#post9092952

Thanks to everyone, I will start checking if there are any broken parts in the intake and replace the spark plugs. I will test and check everything you told me here.

I will bring you new news soon.
Thank you very much.

I've tried checking the intake piece but I can't see much. What I have been able to observe are oil leaks in that area.

If you take off that secondary air pump, you will see it all. Remove the hoses, and I believe it’s 3 T30 screws holding it in plus an electrical connector. That should allow you to see all the rods. The oil leak I’m not too sure on, hopefully someone else on here has an idea. It sounds to me like your intake manifold may be contaminated with oil but I’m not sure.

You could check the PCV on the rear of the engine and see if there’s oil in the hose leading to the throttle body. If there is, replace the drip pan and centrifuge cover. Easy job, just remember that the drip pan bolt is reverse threaded, so you have to twist clockwise instead of counter.

Also, it looks like you may have a leak at your upper radiator hose going to your thermostat. Clean up that crusty coolant and see if it comes back, or if it’s an old leak.

Thank you very much for your quick response. I will remove the air pump to see better. And I'll clean the dry coolant hose and the other thing you told me about.

Update: I actually just removed my secondary air pump to replace the oil filter housing gasket, and it is 5 T30 screws holding it in. Be very careful though, they are different lengths so make sure to make a diagram or something to remember which goes where.

If I have seen it in this YouTube video, thank you.

You should be able to use a flashlight and look down to inspect the front of the intake manifold. use something like an o-ring puller or dental pick and run it along the levers to check if they are still connected. But i guess you can remove the secondary air pump if its in the way.

I replaced the oil filter housing gasket without messing with the secondary air pump. To get the thermostat off I bought a 1/4" drive E10 socket and used a 1/4" drive extension to get the top bolt off. It is a very tight fit, a 3/8" drive socket wont fit without removing the pump.

Surprisingly, I was able to use a 3/8” E10 to get the bolts out on the thermostat. I had to remove the pump because my thermostat housing was very stuck to the block, and it needed a few taps with a rubber mallet to break it loose lol.

Today I took out the air pump and checked the black plastic part and the levers and everything seems to be fine, although I don't know if there could be something wrong inside.



I changed the spark plugs and the car is running a bit better, it doesn't vibrate as much although it still fails and the check engine light is on.

I don't know where to go next, should I use injector cleaner or check the coils?

It’s hard to see much in those videos, but I will take your word for it that the manifold flaps checked out.

What spark plugs did you use? Are the coils still the ones from the factory as well?

As for the fuel cleaner, that can never hurt. Fuel cleaners are really one of the only additives that no one ever debates, they work and they work well. I’ve personally had a lot of good luck with Chevron cleaner, just mix 1oz per gallons of your fuel tank (20oz for us) before you fill up. Let the tank get as empty as you can, throw in the additive, and then immediately fill your tank so it mixes up. Then run that tank fairly close to empty as well before you fill up again to get as much of the cleaning properties as you can before it gets diluted.

I’ve never personally dealt with this or had to dive this deep into the issue, but I personally would be concerned that the internal flaps have snapped off, as it is somewhat common on these engines.

Edit: I reread your original post so here’s what I would do. It will take 5 minutes so give it a shot with the codes reset and see what happens. Take the ignition coil off of cylinder 1 and swap it over with an ignition coil off literally any other cylinder. See if the misfire follows with your swap. If it does, you know you have a faulty coil. It might not fix the whole problem, but it can help narrow it down. I’ll attach a photo of the firing order.

The mechanism of the external flaps worked well and I didn't see anything broken. Although I imagine that to be 100% sure I would have to remove the intake.

The spark plugs that I put in are BOSCH - 0 242 135 509 here is a photo of the change:



I haven't changed the coils for now, I will try what you told me about changing the coil's location.

I will also try to put in some injector cleaner, which I think never hurts.

I have heard of some people having problems using those plugs, but unsure of how true they are. Some people say they had to reset their ECU to make them work properly or something. I went with NGK plugs and they worked great for me. I doubt that it really makes a difference though.

Cali is a boss with extensive knowledge. Diagnosis over the internet is a difficult thing, but I would always exhaust his suggestions until absolutely sure it either is or is not a problem.

All may appear fine on the front of the manifold, but the external levers don't just fail because of plastic heat cycling to a brittle death. They are the sacrificial lamb, giving up the ghost once internal pressures in the manifold cause them to do so. Be glad about this, because that external break is a blessing compared to an internal break with part of a runner breaking off and becoming friends with a valve.

There are 3 sensors on the manifold, it isn't just vacuum telling which runner to actuate when. You can monitor live data and ensure short runners or long runners are doing what they're supposed to when they're supposed to as well as monitoring all things manifold related such as pressure values, temps, etc. It's not discussed as much, but these sensors can also become oil infected like our VVT sensors.

I only bring this up as it's a route to go down and a stone that shouldn't be overturned for the sake of your peace and diagnostic resolution.

Great advice.

Hello again everyone.

I bought a diagnosis, and I changed the coil from cylinder 1 to 2 and the fault was transferred to cylinder 2.

So I think the coil must be defective so I'm going to try buying a new coil, any recommendations?

I had these that I think are the standard ones with 208,000km





Greetings and thanks again.

Delphi GN10235 is what I used for replacement, they’re original equipment. It’s the same as that but just without the Mercedes logo. They’re pretty cheap on RockAuto

Hello everyone,

I’m very happy to say that I have finally solved the problem!

It turned out to be the ignition coil, which failed at 200,000 km.

I have already ordered the remaining five coils.

I was lucky because the issue could have been with the intake or even the ECU, which would have been more complicated and expensive to fix. Fortunately, this was a much simpler and cheaper solution.

I’m sharing the steps I followed in case they help someone else:

1. Replace the spark plugs – In my case, it was time to do so.
2. Check the intake mechanism – By removing the air pump, you can verify that it’s working correctly.
3. Swap the ignition coil location and run a diagnostic test.

Thanks to everyone! My car is running again, even better than before.

Best regards!