[Liquid_Arthur]

Hi,

Been trying to figure this out and made very little progress.

07 335i

It pulls hard and drives like a dream out on the road. What it doesn't do is idle. It idles ok when you first turn it on, as the computer has it idling around 1200 or so. Then it drops to 800, still mostly ok, then when it drops to 600, is where the problems begin. It stumbles, like its about to die, drops to 2 or 300 and then surges to save itself. It does this repeatedly, for most of the time it is idling. Occasionally it does die, stall, like it couldn't rev back up in time.

Once in a while it will sit at 600 for a little bit, nice and smooth, but then, stumbles again.

This is NOT typical N54 idle that I see people posting about, where it blips every 30 seconds or wavers within 100 rpm. This is full on stumble surge repeat.

Makes no difference how long the car has been running or if not at all. I live in Florida so the ambient air temperature is always like 80 degrees plus.

Regarding plugs and coils, it does not feel like a spark miss, I know what those feel like, and this isn't it. Furthermore, just for good measure, my wife has an 08 335i that runs good, so I stole all the coils and plugs out of it, popped 'em in mine and got the same exact stumbling as before. No change.

Also, I just got done walnut blasting the valves. They were diiiiiirty. Same stumbling both before and after. Made no change as far as that is concerned. Of course, it did make the car feel more powerful and responsive when it's moving, but that's hardly my issue today.

I have NO CODES ::cuss cuss cuss::

Well, I have 2AAF Fuel Pump Plausibility, but thats the only code in the INPA and I hear this code is kind of meaningless by itself.

I'd like to try swapping over the fuel injectors from my wife's car but, my INPA, erggggg, it reads error memory but gives me some weird error every time I try to code the injectors. I did manage to reset the adaptions. Does anyone have a link for a good version of INPA?

And please help...!

Thank you,

Liquid Arthur

[HiRev335i]

injectors are a possibility but usually when they are bad and leaking you'll get really rough start ups especially after the car has been sitting like over night. Are you noticing raw fuel smell on morn start ups? As well don't be swapping injectors unless your replacing the Teflon seals they are a one time use only, could run into some serious issues if you don't. At this point I'd try cleaning your vanos solenoids see if that makes a difference if not could be O2 sensor related how many clicks on the car? I see you have a 07 they are notorious for going bad mosfets but usually will eventually throw a cel. I'ts going to be hit or miss without any codes coming up. I'm assuming your using INPA for your diagnostics? I'd start with your solenoids and the replacing O2 sensors if your mileage is high.

[Liquid_Arthur]

139K miles.

I should probably mention, this car is a recent purchase, any previous service history is unknown.

I am in my garage all afternoon, figuring out what I can, I will report back any results.

Never a rough start.

If I turn the AC on so that it idles at 800, it idles smooth as can be...

[HiRev335i]

Originally Posted by Liquid_Arthur

139K miles.

I should probably mention, this car is a recent purchase, any previous service history is unknown.

I am in my garage all afternoon, figuring out what I can, I will report back any results.

Never a rough start.

If I turn the AC on so that it idles at 800, it idles smooth as can be...

At 139 K if never done your about due for O2's ……..good luck

[Liquid_Arthur]

Finally it threw some codes, for low pressure fuel sensor and fuel pump. I am going to check into this, hopefully that will correct it.

[mweisdorfer]

Originally Posted by Liquid_Arthur

Hi,

Been trying to figure this out and made very little progress.

07 335i

It pulls hard and drives like a dream out on the road. What it doesn't do is idle. It idles ok when you first turn it on, as the computer has it idling around 1200 or so. Then it drops to 800, still mostly ok, then when it drops to 600, is where the problems begin. It stumbles, like its about to die, drops to 2 or 300 and then surges to save itself. It does this repeatedly, for most of the time it is idling. Occasionally it does die, stall, like it couldn't rev back up in time.

Once in a while it will sit at 600 for a little bit, nice and smooth, but then, stumbles again.

This is NOT typical N54 idle that I see people posting about, where it blips every 30 seconds or wavers within 100 rpm. This is full on stumble surge repeat.

Makes no difference how long the car has been running or if not at all. I live in Florida so the ambient air temperature is always like 80 degrees plus.

Regarding plugs and coils, it does not feel like a spark miss, I know what those feel like, and this isn't it. Furthermore, just for good measure, my wife has an 08 335i that runs good, so I stole all the coils and plugs out of it, popped 'em in mine and got the same exact stumbling as before. No change.

Also, I just got done walnut blasting the valves. They were diiiiiirty. Same stumbling both before and after. Made no change as far as that is concerned. Of course, it did make the car feel more powerful and responsive when it's moving, but that's hardly my issue today.

I have NO CODES ::cuss cuss cuss::

Well, I have 2AAF Fuel Pump Plausibility, but thats the only code in the INPA and I hear this code is kind of meaningless by itself.

I'd like to try swapping over the fuel injectors from my wife's car but, my INPA, erggggg, it reads error memory but gives me some weird error every time I try to code the injectors. I did manage to reset the adaptions. Does anyone have a link for a good version of INPA?

And please help...!

Thank you,

Liquid Arthur

Check the vac line at the throttle body

[Liquid_Arthur]

Originally Posted by mweisdorfer

Check the vac line at the throttle body

That's a really good idea! I assume I should be checking it for leaks, but what exactly should I be looking for or how should I be testing?

[relative4]

Smoke test.

[mweisdorfer]

Originally Posted by Liquid_Arthur

That's a really good idea! I assume I should be checking it for leaks, but what exactly should I be looking for or how should I be testing?

Just make sure it's connected & not broken

[andrew.nottingham]

A quick test, before a smoke test or checking vacuum lines, is to unplug the maf. I've dealt with multiple cars with similar issues; misfires at idle, surging idle, etc. These cars ran beautifully with the MAF unplugged, and this was due to a vacuum leak.

When there's a vacuum leak, there is more air entering the engine than the MAF sensor detects, so the car runs like crap.

Try unplugging the maf and see what happens

[dannyjones]

When I had stumbles like that it was the HPFP. I never had problems whilst driving. It got worse and worse over a year or two and I finally got a fuel pressure code and limp mode one day. No issues after replacing hpfp. But mines a 2011 N55

[relative4]

Originally Posted by andrew.nottingham

A quick test, before a smoke test or checking vacuum lines, is to unplug the maf. I've dealt with multiple cars with similar issues; misfires at idle, surging idle, etc. These cars ran beautifully with the MAF unplugged, and this was due to a vacuum leak.

When there's a vacuum leak, there is more air entering the engine than the MAF sensor detects, so the car runs like crap.

Try unplugging the maf and see what happens

Gonna unplug the MAF on an '07 335, are ya?

[dpaul]

FWIW, there is no MAF (mass air flow) sensor on the N54 engine. There are two MAPs (manifold absolute pressure) sensors - one of them is on the intake manifold and the other, called the TMAP because it also measures temperature, is on the charge pipe.

Also, to the point of the previous poster, you can unplug the MAP (the one on the manifold) and the engine will run quite well. I wouldn't leave it this way but there is no immediate consequence other than more error codes.

[mweisdorfer]

Originally Posted by andrew.nottingham

A quick test, before a smoke test or checking vacuum lines, is to unplug the maf. I've dealt with multiple cars with similar issues; misfires at idle, surging idle, etc. These cars ran beautifully with the MAF unplugged, and this was due to a vacuum leak.

When there's a vacuum leak, there is more air entering the engine than the MAF sensor detects, so the car runs like crap.

Try unplugging the maf and see what happens

There isn't a MAF in a 335i.

[andrew.nottingham]

Originally Posted by mweisdorfer

There isn't a MAF in a 335i.

hah my apologies. i am not a bmw expert at all, i have just worked on many other cars and know that this works when there is a post-maf leak. I'm sorry for giving bad advice!

[Liquid_Arthur]

Originally Posted by andrew.nottingham

hah my apologies. i am not a bmw expert at all, i have just worked on many other cars and know that this works when there is a post-maf leak. I'm sorry for giving bad advice!

It's all good, I had a spare MAF from my old E46 in the garage so I unplugged that one, it didn't help :-(

Im joking, I appreciate the good intent regardless.


So, I finally had a chance to take a look at a few more things and...

Well I smelled some fuel near the back. Pull off my back seat and whaddayaknow, there's fuel all over the top of the fuel pressure regulator and dripping down the back of the tank. Now I'm no rocket surgeon but I'm pretty sure the fuel goes IN the tank and not on top of it. So I ordered a new fuel pressure regulator and that is going to fix this!

[Liquid_Arthur]

Well, I did that and it fixxed the leak, but not the idle. Erg. I guess I need to look into doing a smoke test. Does anyone have a link to a good write up for one? Any other ideas?

[arkie6]

I've seen several youtube videos on smoke testing a 335i.

[relative4]

Pretty straightforward. Remove the air box, plug one inlet, smoke in the other.

[Liquid_Arthur]

Originally Posted by relative4

Pretty straightforward. Remove the air box, plug one inlet, smoke in the other.

Ok, I think I can work with that. Now to pick a flavor of Swisher...

[Liquid_Arthur]

My wife and I tried a rudimentary smoke test last night and found nothing. I've been watching videos on youtube about the smoke test, but none of them seem that good. Is the intent of the smoke test to find boost leaks? Or any leaks? As the previous poster said, plug one side, blow smoke in the other, and then look for leaks. Maybe we didn't have enough smoke, but we did not see any smoke coming out. Am I missing something? Any other ideas?

It idled fine at 600 RPM for over 3 minutes the other night, then sure enough, started stumbling again.

Im going to pull my hair out.

[macheff03]

I had a similar problem on my n52-
At least it sounds similar- rough idle, surging, etc...

Anyway what fixed it for me was just cleaning the VANOS solenoids- there are two.

Very easy to do- maybe 30 minutes or so

Certainly made it much better!
May be worth a try- after all it is free

If you don't know how just google a video there's plenty out there...

Good luck