M42 Engine Bogging/Laggin Under Acceleration - HELP ME

[Metallated]

Hey r3v, so about a month ago my 318 started having trouble under acceleration; bogging down and stuttering.

Initially I thought it was a bad clutch that wasn't catching, so I replaced it and the slave cylinder..

Looking back that clearly wasn't the cause, but it was going to need to be done sooner or later.

I did a stomp test and got the code for amf, 1215, and the car wasn't starting. I replaced the fuse for the amf and the car started up, but it still stuttered under acceleration and when warm idled rougher aswell, it still reports the 1215 code, and I'm not sure if the code goes away once the issue has been addressed?

I'm really at a loss here and have no idea what the issue is, I'd appreciate any insight into what I should address and replace, Thank you.

[bmwman91]

It sounds like it could be your AFM. The little carbon track inside wears out and ends up "skipping" which essentially tells the ECU that there is no air coming in, so it cuts fuel. Is the bogging pretty consistent in terms of the RPM and load conditions under which it happens?

You can clean & repair the AFM pretty easily yourself as long as you care careful. Or, you can try to find a local member with one for you to borrow.

[Metallated]

It sounds like it could be your AFM. The little carbon track inside wears out and ends up "skipping" which essentially tells the ECU that there is no air coming in, so it cuts fuel. Is the bogging pretty consistent in terms of the RPM and load conditions under which it happens?

You can clean & repair the AFM pretty easily yourself as long as you care careful. Or, you can try to find a local member with one for you to borrow.

Thank you so much for the prompt reply, I really appreciate your insight.

The bogging is consistent throughout the rev range and is noticeable at idle but intensifies under load.

I checked the paddle in the afm to ensure it moved freely, which it did, but I will look into cleaning this carbon track which you describe?

[bmwman91]

Carefully pop the plastic cover off of the AFM and get a look inside. You can post pics if you want additional input. The AFM really is not all that fragile, so don't be afraid to pry the lid off and poke around. As long as you do not bend the little copper wiper arm, change the torsion spring position or gouge the carbon track you will be OK. See this thread for good photos of the guts of an AFM and what goes wrong (the M42 one is a little different and fairly easy to repair yourself...Youtube has some videos).

http://www.r3vlimited.com/board/showthread.php?t=247831

Putting the cover back on is fairly straightforward and just requires some electronics-safe RTV adhesive (NEVER use one with acetic acid solvent as it will corrode electronics, look for one with alcohol as the solvent or which at least says it is safe on electronics...it should be pretty easy to find at the local parts store). Obviously use it sparingly so it does not get onto the electronics when you reassemble.

[Metallated]

Carefully pop the plastic cover off of the AFM and get a look inside. You can post pics if you want additional input. The AFM really is not all that fragile, so don't be afraid to pry the lid off and poke around. As long as you do not bend the little copper wiper arm, change the torsion spring position or gouge the carbon track you will be OK. See this thread for good photos of the guts of an AFM and what goes wrong (the M42 one is a little different and fairly easy to repair yourself...Youtube has some videos).

http://www.r3vlimited.com/board/showthread.php?t=247831

Putting the cover back on is fairly straightforward and just requires some electronics-safe RTV adhesive (NEVER use one with acetic acid solvent as it will corrode electronics, look for one with alcohol as the solvent or which at least says it is safe on electronics...it should be pretty easy to find at the local parts store). Obviously use it sparingly so it does not get onto the electronics when you reassemble.

Thanks for the info, I will pop the cover off and take some pics tomorrow evening, you offer of looking at it would be excellent. I found a video and will look at the thread you linking in the mean time, thanks for the resource..

My concern is I feel if issue was the track wouldn't the hesitation only be at one point? Mine occurs from idle to above 2K

[othatseric]

I had the same code a while back, I did change quite a bit of stuff tho.. message me I can let me know the specifics from what I remember -- I do suggest taking off the intake manifolds and cleaning them out liberally, especially the lower manifold, gaskets too. Also check the resistance of the blue coolant temp sensor is within spec as well. Good luck!

[Metallated]

I am hesitant to blame the issue on the carbon track due to not being able to see metal.

What about the intake air temperature sensor? The issue seems worse once the engine is warm...

[Metallated]

So I just cleaned off and bent the prong for the tempo sensor back into position and it is better but still hesitates, just not so jumpy.. I might try cleaning it better and just buy a new one if that doesn't fix it.

[bmwman91]

The small part of the track that is visible does look a bit manky. So yeah, lik eyou mentioned, clean a little more and try to move the wiper prong to a different enough part of the radius to avoid the damage. You can get a can of electrical contact cleaner and spray out the inside (take the AFM out, hold it upside down and shoot it out with contact cleaner).

[Gregs///M]

Cleaning the inside of the AFM will not do much because its sealed from the electronics section of the AFM. Not just the wiper arm but all those contacts can have copper oxidation from 30 years of siting in the engine bay. Unfortunately, the M42 is much more difficult and fragile to open and clean than the rest of the AFM's used by BMW. With that said, complete disassembly of the AFM is recommend so that copper can be cleaned, and as you can see from your AFM, that is no easy task.

M42 AFM's in new or rebuilt condition are very hard to come by so another option is our rebuild service. Its $185 shipped and takes about 30 days. We do AFM service for clients globally including many race teams across the country.

[Gregs///M]

I should also note, a very real possibility is the main culprit could be vacuum leaks, which are way more common failure.

[Metallated]

Thanks for the input guys! I will definitely look into your rebuild service. And I'll certainly check for vacuum leaks.

I am not talking about the internals in the black box however, rather the actual sensor part below:

[bmwman91]

The IAT thermistor should be fine. They are super duper simple little devices and it is (I would guess) rare for them to fail. You can test it fairly easily with a multimeter. Check the resistance and shake the sensor / gently poke the thermistor with a pencil eraser to see if the value jumps.

If it is dead, I know of a part on Digikey that has the exact same temperature-resistance function. You would need to do some serious disassembly and soldering, but you could actually replace the thermistor for about $0.25. I may even have some extras from my MAF conversion and I could send you one.

As Gregs///M notes, it could very well just be a vacuum leak. There are lots of places on the M42 for them to show up.