e46 M3 - Dies at Idle / accelerating from a stop (intermittent) (SOLVED WITH UPDATE)

[ChapterM3]

Hey everyone -

I'm writing this at 12:50am, I just got back from a job which I'm working 16 hour days at the moment and will for the entire rest of the week. Of course the M3 decides that this is the best time to give me the following issue when I need it the most, it needs some TLC.


From the 20 minutes of half opened eye searching I've done, this is what I think is going on, let me know if you've had this issue before and what you've done to fix it/diagnose it further before buying random parts -


Here's what's going on -


The situation tonight:

Started it up as usual (cold) - after idling for 15 seconds, all of a sudden, it just stuttered and died. Started it back up, no problem. Ran it on 95 for 25 minutes back to Boston. Got off highway, stop at second stop light, accelerating away slowly, car dies in middle of an intersection. Turns over but does not start for 10 seconds. Thought I might have to tow, then finally it starts on 4th try of turning key all the way over.


Other helpful info:

• No CEL, EML or codes, scanned it with my wifi dongle
• No other idle issues/misfires - car drives like normal, then this happens out of the blue

Possible diagnosis from 20 min of research:

• Intake cam position sensor?
• Bad gas? (Just filled a new tank, same place as always though)
• Fuel pump?

Thanks for the helpful responses!!

Jonathan

UPDATE - The solution ended up being all 4 things: Intake and Exhaust camshaft sensors and the fuel pump + relay.

[FBloggs]

The hard starting, could be the crank position sensor; It is not bad enough to throw a hard code.
The crank sensor is much easier to replace.
When mine stalled coming to a stop, a new intake cam sensor sorted it.
there was a BMW code 50.

[dukeofchen]

Unfortunately a dying fuel pump also tends not to throw a code. But based on what FBloggs said the crank position sensor might be a more likely place to start.

When mine finally went the engine stalled as I came to a stop to make a right turn, then wouldn't start at all after. If your fuel pump is on its way out there likely would have been other issues with hesitation due to weak fuel flow / pressure, running out of gas at 1/4 tank, etc., instead of a binary start / no start condition.

[bigjae46]

Sounds like an idle air issue. on cold starts, the engine starts on throttle air and then transitions to idle air.

Idle air valve might be stuck closed.


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[jet_dogg]

I love how 50% of these threads are in search of internet mechanics haha.

Shows what a resource a good forum is.

[FBloggs]

I love how 50% of these threads are in search of internet mechanics haha.

Shows what a resource a good forum is.

If you want to run an E46 M3, you need a code reader, and some guessers, lol.
Each issue the car exhibits has a chain of causative factors.

[jet_dogg]

Or you could just change things in a timely manner.

[jbfrancis3]

I like your 3rd guess, the fuel pump.

[ChapterM3]

Crank case sensor and the fuel pump is what I've gathered so far - with a feeling of the crank sensor more. I'll see if I can't run the car a bit today to see if it throws any codes. Absolutely need a reader - I have one that is a USB wifi dongle, but it has only told me the car has no codes right now. The shop I typically go to is booked out until mid September so I'm stuck right now trying to diagnose this myself which is a pain.

I'll continue the search. This is part of the maintenance work absolutely, I've been trying to stay ahead of it and replace things as I feel they need - is there any guide of when to replace what at what time? So kind of like a "once the car hits 150k this is what you could consider replacing?" type guide?

[jbfrancis3]

If its approaching 150k and you rely on it, putting in a fuel pump wouldn't be a waste of money. Could you tackle it yourself?

[jet_dogg]

Replace everything at 150k.

[dukeofchen]

Crank case sensor and the fuel pump is what I've gathered so far - with a feeling of the crank sensor more. I'll see if I can't run the car a bit today to see if it throws any codes. Absolutely need a reader - I have one that is a USB wifi dongle, but it has only told me the car has no codes right now. The shop I typically go to is booked out until mid September so I'm stuck right now trying to diagnose this myself which is a pain.

I'll continue the search. This is part of the maintenance work absolutely, I've been trying to stay ahead of it and replace things as I feel they need - is there any guide of when to replace what at what time? So kind of like a "once the car hits 150k this is what you could consider replacing?" type guide?

This is more or less gospel around here: https://nam3forum.com/forums/forum/m...ockdown-thread

I feel your pain having bought my car without much in the way of service history. Feels like right when I see the light at the end of the tunnel, the next thing rears its head. Still intend to keep this thing forever though.

I love how 50% of these threads are in search of internet mechanics haha.

Shows what a resource a good forum is.

Especially when there's two decades of searchable archives...ah shit.

[Lukem3]

Sounds like an idle air issue. on cold starts, the engine starts on throttle air and then transitions to idle air.

Idle air valve might be stuck closed.


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+1 to idle issue. From expierence a bad cam sensor will cause other drive ability issues, not saying its unlikely but there's other more likely scenarios. I would start looking into the icv. Check the ccv for any vacuum leaks, same with the itbs.
Cleaning the throttle bodies, injectors and icv would be a great place to start. If spark plugs are past due swap them out instantly. Whether its the iasue or not at 150k the theottle bodies are goinf to be toasty. Perform an adaptation reset and throttle relearn after. If you're still having issues and no vacuum leaks are found, vanos could be starting to fail causing it to stall or a fuel issue. Live pid monitoring or testing for fuel pressure would be the next course of action. The dme is good at monitoring the crank and cam sensors, you'd most likely have a code for them or even for timing.

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[mittortz]

Crank case sensor and the fuel pump is what I've gathered so far - with a feeling of the crank sensor more.

How did you end up resolving? Your initial post describes my issue exactly. Would really appreciate anything you found out. I'm about to order a fuel pump regardless - can't decide if I should pay $500 for BMW or $100 for Hella (from bimmerworld with 2 year warranty). But still not sure if that will fix. I'm also planning to clean the ICV tomorrow... Never even thought about the crank case sensor. Is that the same as the CCV? Any insight you have would be super helpful, my M3 died on me in the middle of a house-move, so I'm praying for a quick fix. Super stressed atm lol.

[ChapterM3]

How did you end up resolving? Your initial post describes my issue exactly. Would really appreciate anything you found out. I'm about to order a fuel pump regardless - can't decide if I should pay $500 for BMW or $100 for Hella (from bimmerworld with 2 year warranty). But still not sure if that will fix. I'm also planning to clean the ICV tomorrow... Never even thought about the crank case sensor. Is that the same as the CCV? Any insight you have would be super helpful, my M3 died on me in the middle of a house-move, so I'm praying for a quick fix. Super stressed atm lol.

Oh man sorry to read this! It ended up being a combination of things: Intake and Exhaust camshaft sensors and the fuel pump/relay. My mechanic at the time diagnosed it thoroughly (he's been a friend of mine since kindergarten so I knew he wasn't trying to sell me on all of them), and recommended that we do them all at once. I'll update the original thread as well.

I hope this helps you!!