MAF code

This sounds like you have a dirty throttle bore, here is a guide that will help you fix the problem. Also, can you remove the MAF connector to see if there is any corrosion or damage?

https://www.2carpros.com/articles/throttle-actuator-service

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.

What is the actual code? There are a couple things about diesel engines that will cause this.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

However, we need to know the code so that we can be sure this is the same thing that I am thinking it is.

Basically, what happens on these is the manifold gets soot in it and it is restricted so the PCM thinks there is a MAF sensor issue, but it just can't breathe.

So, cleaning the EGR is a good thing but more than likely there is already soot in the intake and that is going to have to be cleaned as well.

What you mean soot as in carbon build up and gunk?

I had code 4c04 for the EGR but it's not back anymore. The MAF code is 3FF1.

Perfect. Yes. These codes indicate restricted air flow. So, what I would do is remove the tube from the turbo to the intake and see if there is any build up.

Yes. Soot is the natural byproduct of diesel engine combustion. If you remember the black smoke that diesel trucks use to emit, this is soot. So now all that needs to be captured but it gets into the EGR system and eventually can get into the intake, and it will restrict the intake.

Take a look at the info below and let's start with the first code and check the things listed in the action in service section.

I can't believe a hose would do that, i would be surprised if it had that much soot. What about the intake itself since it has many small pores for airflow? Or is the code indicating that the blockage kf air is even before it reaches the intake? I will check the hose for sure though.

Okay. I agree, however, seeing what is in that hose will be telling as to what the issue is. To answer your question, yes, it is rare that it is just the hose but that will be a sign as to what is going on.

If you find soot, there then you will have more in the intake and that is going to restrict the air flow and make the PCM think the MAF is just wrong.

Basically, the engine can't tell that there is soot build up causing a restriction, so it thinks that the MAF is wrong.

So that code does not tell you where the restriction is only that the MAF is showing low air flow. Just experience with diesel engines is what tells us that this is likely the cause.

Thanks, very valuable info, I will check it and let you know.

hopefully the hose is not pain to remove.

Haha. Yeah. I am not sure as I have not done that on these vehicles but it is a BMW so I would bet it is.

I am attaching the info on this but there is a good amount of detail on cleaning the intake system and plenum so clearly BMW is aware of the need to do this. I am thinking that the swirl valve are going to be the root cause of this. When they get covered in soot, they stick and will restrict the air flow as well. If this is the case, the entire intake needs to be cleaned.

BMW says to use a wand to reach down the intake and you basically media blast the engine clean.

The tube looked clean. I also replaced the MAF with another diesel i have. I got code 4B81 for erg deviation and reduced speed, deleted it and came back.

If i disconnect the harness on ERG to see if it will do it again, will that work?

Or disconnect the mass and see? Here are some readings while running and everything connected.

When it is running does it seem to have full power? I am thinking the exhaust may be clogged.

Yes, has full power, very powerful, only reduced power when the code comes on, driven it 100 miles, power on this turbo is amazing.

Is the boot between the MAF and the throttle bore in good shape? No leaks?

I will double check again.

There is a big turbocharger intercooler that was so dirty on the outside both sides, pressured washed it and put it back. There is only one boot from mad to cooler and its clean, same from cooler to the one going to throttle body. Now I am getting 4bc6 and 4bc2. Dang MAF won't stay in place keeps coming out of the rounded piece. I didn't mess with it, i only removed the whole thing when i tried to replace it. Also, the temperature sensor moves and I am not sure it is supposed to or not.

I did not even touch the intake sensor for it to give me a code, what the heck.

Solved, i think. The codes and check engine light were coming on immediately after starting cR, you delete then and come right back immediately. Followed the charge pipe and there was the air sensor which refs between it and MAF to get right readings. It had a lot of oil on it. Carb cleaner and its done. Started and drove it didn't come back so far.

Okay. That is great. Just put some miles on it and then recheck the sensor to see if there is more oil getting on it. There should not be oil in the charged air system so if there is then this normally means the turbo is leaking. There is oil supplied to the turbo to keep it cool and lubricated and it seals this from the charged air side of the intake. So, if you have oil in there then that normally means the turbo is leaking and allowing oil into the intake.

You would have to replace the turbo for this unless there is a rebuild kit.

However, that is definitely the issue so hopefully it doesn't return.

Yes, sir, thanks.

All is good still but i noticed there is a slip to hold the air charge temperature sensor that broke while i put it in. can you find for me if this is a piece that can be purchased? It basically just holds the sensor onto the pipe and keeps sensor in place

Can you get a picture of the piece that you are looking for? I am only showing that the sensor is held in by two screws. Must be the wrong one.

No screws, the air charge sensor is in the aluminum pipe on the passenger side. The pipe starts at throttle body as a hose then connects to this pipe via a plastic connector. I think i found it online. Called BMW twist protection part # 11617807095.

Got it. Yep. That looks like it. Thanks for adding that detail.