[suspect]

I have been trying to figure out what is wrong with my cars idle. I dont know if it is normal. The car idle stumbles a little here and there. There are no codes. There is no RPM fluctuation but you can just feel it in the seat. Yesterday I heard a pop misfire for the first time from a cold start.

Before this I had one bad injector. The spark plug was not wet or fuel smelling at all but it was dark. After changing that injector, no more dark spark plugs. All other spark plugs are always dry, the car never has trouble starting first time after sitting for a few minutes, hours or days. The fuel rail pressure ranges between 6-700 psi to 2000 psi depending on driving condition.

Compression test results for a cold engine are cyl 1-6 = 175, 165, 170, 160, 170, 165 (psi). Only moved the car around then turned it off before test.

New coils, spark plugs, premium fuel, walnut blast, hpfp replaced about 15k ago.

Bank 2 LTFT is always negative at idle. Started at -7% before injector change and now it is around -2 to -3% after walnut blast. Should I reset adaptations?

After the walnut blast the idle hiccup/stumble in the exhaust sound has become inconsistent on cold starts. I tried to record the sound in the morning but it was smooth. Sitting in the seat you can always feel the stumble/slight shake here and there, its not constant in the short term. The exhaust stumble becomes more prominent if car is warm. I had a VANOS code, cleaned the solenoids, swapped them around and no VANOS codes since under same driving conditions. No change. I do have a wastegate rattle and waiting for it to throw 30FF code to change turbos.

The best video I can find is this, notice how the exhaust stumbles. Mine is not this bad. Is this normal for this engine? In almost all other videos the sound is smooth.
https://www.youtube.com/shorts/F-o6J2Y9oEM



Picture of old spark plugs before injector change. Red circle is for cylinder with bad injector.

[suspect]

Anyone? What’s the normal idle like for this engine?

[AWD Addict]

This car has a finicky fuel system, which can cause these things. Early on, BMW had issues with fuel pumps and injectors, which many people had replaced many times under warranty. Checking you have all the updated parts is a good start.

But even with all those things perfect, I still have occasional stutters at idle, particularly on cold starts. it sometimes feels like bad tanks of gas because it's not consistent.

There are lots of posts on this. Enjoy the reading. There are a million things from a cracked valve cover or charge pipe, bad injectors, coil packs, dirty intake valves, etc. it can turn into a wild goose chase quickly.

[studio54]

Mine is doing the same, it seems to be common on the N54.

Very tiny hiccups once in a while while idling, felt in the cabin. Some ppl just raise the idle with MHD to 800rpm or something. (Notice if when AC is on there is almost no hiccups cause the idle is higher? On mine it's the case, after spirited driving or with the AC, it's idle at around 800 rpm+ and no hiccup anymore)

I use Bosch OEM 4 prongs, but I read more than once that BMW stamped from the dealer aren't exactly the same (very minor difference or factory defect with the gap on Bosch OEM).

I am not saying that this will resolve the issue, but a guy was having the tiny hiccups with brand new Bosch OEM, then swapped with original old ones, and no hiccups anymore.

My next plugs set will be NGK with the gap to see if it's better.

Thread : https://www.e90post.com/forums/showthread.php?t=571344

"After weeks of troubleshooting my rough idle E93 N54 I managed to solve mine. Tried everything discussed on these threads including walnut blasting the intakes, coils, cleaning electrical connectors, etc. and nothing worked. As a last resort I decided to put back the old spark plugs and voila - car runs good as new much to my surprise. Here's what I learned through the process that I thought i'd share with the forum in case it can help others. I had a bit of a rough idle a few weeks ago for which I started with new plugs from Amazon. The plugs were new OEM BMW BOSCH 4 electrode plugs and were exactly the same part number as what was in the car - even the stamping on the side was exactly the same including the "made in germany" part. There was no reason to suspect any issues with these plugs. During the change I also added a catch can and replaced a spark plug heat shield tube on #3 cylinder which had what appeared to be corrosion on it i.e. crusty green deposits. What I later learned is that corrosion is linked to spark arcing through the coil insulator to ground through the spark plug heat shield. Not all BMW's use this heat shield but it appears to be common on Turbo cars - down side to them is that they provide a good ground very close to the coil stem which can allow the spark to jump out. Once it starts the insulator deteriorates and issue gets worse. The corrosion is ionized air on the aluminum sleeve. It also deposits on the coil stem so keep a watch for these and clean (or preferably replace) these coils as needed. I suspect this was the initial reason for my rough idle but by putting in new plugs I managed to move the problem and cause weeks of headaches trying to troubleshoot. Now back to the plugs - after close inspection of the new plugs the only physical difference appears to be the gapping of the 4 electrodes. One or two electrodes on the new plugs appear to be closer to the center pin than the old ones. Remember - these are factory gapped plugs and not intended to be re-gapped by the user. I figured the larger gaps was wear on my old plugs and decided not to address it on the new ones. After about 500Km of horrible idling and lots of troubleshooting I swapped back to the old plugs as a last resort. I examined the new ones and found the ones with the small gaps had burn marks only one side of the porcelain insulator. That a sign that three other electrodes were likely not firing. All that to say - I believe short of an internal issue with the new plug (i.e. manufacturing defect) the root cause is the smaller gap on some electrodes causing an insufficient spark for proper detonation especially on idle. That likely explains why the computer does not detect a fault and why certain conditions like load from the AC compressor or engine/ambient temperature vary the symptoms. Since switching back to the old plugs the car is running perfect. If I find some time I plan to pull the old plugs again and measure the gaps then regap the new plugs somehow to match and try them again. If that works then this will tell for certain the gap is the root cause and not a plug manufacturing defect. Another key lesson here is to pay close attention to the details and part conditions. You could replace all coils, plugs, injectors and hope for the best but in my case that would have addressed the arcing coil issue and not the faulty plug gap. I would have thrown out lots of good parts and money in the process and I hate doing that because you never get to actual root cause and you waste lots of money. If the rough idle returns, I would keep a close eye the coil stems and plug heatshields. If it happened to one, it's likely going to happen to one of the other 5 and it will leave a crusty deposit as a telltale sign. Will also need to be much more careful with spark plugs - I might try NGK's as I'm told some newer BMW's come with those from factory now. Check the gaps! Hope this helps in case you are dealing with the same issues."

[suspect]

Originally Posted by AWD Addict

This car has a finicky fuel system, which can cause these things. Early on, BMW had issues with fuel pumps and injectors, which many people had replaced many times under warranty. Checking you have all the updated parts is a good start.

But even with all those things perfect, I still have occasional stutters at idle, particularly on cold starts. it sometimes feels like bad tanks of gas because it's not consistent.

There are lots of posts on this. Enjoy the reading. There are a million things from a cracked valve cover or charge pipe, bad injectors, coil packs, dirty intake valves, etc. it can turn into a wild goose chase quickly.

It is exactly a wild goose chase now. It could be the injectors but which one? I looked at rough running in INPA and the cylinders with old 5 injectors behave like the one with the new injector. I am hesitant to take them out and do a test because the plastic tab holding the connectors are very brittle. I also read on some people fixing this problem with original BMW or NGK spark plugs instead of the oem recommended bosch spark plugs. I am not sure if that is masking the problem or it really is spark plugs or maybe its just the way some N54s are.

[suspect]

Originally Posted by studio54

Mine is doing the same, it seems to be common on the N54.

Very tiny hiccups once in a while while idling, felt in the cabin. Some ppl just raise the idle with MHD to 800rpm or something. (Notice if when AC is on there is almost no hiccups cause the idle is higher? On mine it's the case, after spirited driving or with the AC, it's idle at around 800 rpm+ and no hiccup anymore)

I use Bosch OEM 4 prongs, but I read more than once that BMW stamped from the dealer aren't exactly the same (very minor difference or factory defect with the gap on Bosch OEM).

I am not saying that this will resolve the issue, but a guy was having the tiny hiccups with brand new Bosch OEM, then swapped with original old ones, and no hiccups anymore.

My next plugs set will be NGK with the gap to see if it's better.

Thread : https://www.e90post.com/forums/showthread.php?t=571344

"After weeks of troubleshooting my rough idle E93 N54 I managed to solve mine. Tried everything discussed on these threads including walnut blasting the intakes, coils, cleaning electrical connectors, etc. and nothing worked. As a last resort I decided to put back the old spark plugs and voila - car runs good as new much to my surprise. Here's what I learned through the process that I thought i'd share with the forum in case it can help others. I had a bit of a rough idle a few weeks ago for which I started with new plugs from Amazon. The plugs were new OEM BMW BOSCH 4 electrode plugs and were exactly the same part number as what was in the car - even the stamping on the side was exactly the same including the "made in germany" part. There was no reason to suspect any issues with these plugs. During the change I also added a catch can and replaced a spark plug heat shield tube on #3 cylinder which had what appeared to be corrosion on it i.e. crusty green deposits. What I later learned is that corrosion is linked to spark arcing through the coil insulator to ground through the spark plug heat shield. Not all BMW's use this heat shield but it appears to be common on Turbo cars - down side to them is that they provide a good ground very close to the coil stem which can allow the spark to jump out. Once it starts the insulator deteriorates and issue gets worse. The corrosion is ionized air on the aluminum sleeve. It also deposits on the coil stem so keep a watch for these and clean (or preferably replace) these coils as needed. I suspect this was the initial reason for my rough idle but by putting in new plugs I managed to move the problem and cause weeks of headaches trying to troubleshoot. Now back to the plugs - after close inspection of the new plugs the only physical difference appears to be the gapping of the 4 electrodes. One or two electrodes on the new plugs appear to be closer to the center pin than the old ones. Remember - these are factory gapped plugs and not intended to be re-gapped by the user. I figured the larger gaps was wear on my old plugs and decided not to address it on the new ones. After about 500Km of horrible idling and lots of troubleshooting I swapped back to the old plugs as a last resort. I examined the new ones and found the ones with the small gaps had burn marks only one side of the porcelain insulator. That a sign that three other electrodes were likely not firing. All that to say - I believe short of an internal issue with the new plug (i.e. manufacturing defect) the root cause is the smaller gap on some electrodes causing an insufficient spark for proper detonation especially on idle. That likely explains why the computer does not detect a fault and why certain conditions like load from the AC compressor or engine/ambient temperature vary the symptoms. Since switching back to the old plugs the car is running perfect. If I find some time I plan to pull the old plugs again and measure the gaps then regap the new plugs somehow to match and try them again. If that works then this will tell for certain the gap is the root cause and not a plug manufacturing defect. Another key lesson here is to pay close attention to the details and part conditions. You could replace all coils, plugs, injectors and hope for the best but in my case that would have addressed the arcing coil issue and not the faulty plug gap. I would have thrown out lots of good parts and money in the process and I hate doing that because you never get to actual root cause and you waste lots of money. If the rough idle returns, I would keep a close eye the coil stems and plug heatshields. If it happened to one, it's likely going to happen to one of the other 5 and it will leave a crusty deposit as a telltale sign. Will also need to be much more careful with spark plugs - I might try NGK's as I'm told some newer BMW's come with those from factory now. Check the gaps! Hope this helps in case you are dealing with the same issues."

I need to pay attention to high warm idle (~800RPM) next to see if it stumbles. The bosch plugs I have right now are three prongs not four. I paid close attention to the inside ignition/spark plug wells and there was no hint of corrosion on the heat sheilds they looked in good shape. I found similar threads to the one you gave a link to from a few years ago where this random slight stumble was fixed with BMW spark plugs or NGK spark plugs. That will be on my to do list for next service. If there is a bad injector I want to find it soon and change it but theres no indication of bad injectors.

Maybe its natural for this engine to be not as smooth. I6 engines are meant to very smooth.

[AWD Addict]

Originally Posted by suspect

It is exactly a wild goose chase now. It could be the injectors but which one? I looked at rough running in INPA and the cylinders with old 5 injectors behave like the one with the new injector. I am hesitant to take them out and do a test because the plastic tab holding the connectors are very brittle. I also read on some people fixing this problem with original BMW or NGK spark plugs instead of the oem recommended bosch spark plugs. I am not sure if that is masking the problem or it really is spark plugs or maybe its just the way some N54s are.

I know it's frustrating. I'd consider going with an mhd tune because of how robust the data logging features are.

I'm going to ngk one step colder plugs at my next service. My oe bosch plugs have about 10k miles on them (stage2+) and I'm hoping I can edge down IATs a bit with them. I've heard even BMW is using them now OE because the bosch weren't consistently good. I've heard a lot about gapping issues with the three prongers.

Consider a smoke test. It's a cheap way to eliminate leaks as part of the problem. Between that, checking for leaky injectora and minding your gas selection, you can cover a lot of area for low dollars first.

[studio54]

Originally Posted by suspect

I need to pay attention to high warm idle (~800RPM) next to see if it stumbles. The bosch plugs I have right now are three prongs not four. I paid close attention to the inside ignition/spark plug wells and there was no hint of corrosion on the heat sheilds they looked in good shape. I found similar threads to the one you gave a link to from a few years ago where this random slight stumble was fixed with BMW spark plugs or NGK spark plugs. That will be on my to do list for next service. If there is a bad injector I want to find it soon and change it but theres no indication of bad injectors.

Maybe its natural for this engine to be not as smooth. I6 engines are meant to very smooth.

Yes, it's a fast test, pull AC ON, check your idle is at least at 800 rpm and let it idle one minute or two to see if it will still have a tiny one.

My bad, I also use 3 prongs Bosch (0242140507), I said 4 prongs because of the text I quoted that induced me to say something wrong. (I don't even know if there are 4 prongs plugs for the N54 ?!?)

Me too, next set, NGK (need to buy the gapping tool I guess...)

[E93Seattle (Racerbruce)]

i too had an intermittent miss below 2k rpm's and while installing an aluminum chargepipe, bov, jb+ plug & play software, aluminum billet pcv i installed ngk iridium 2 step colder plugs, dinan performance spark plug coils and the intermittent idle disappeared; it's been nearly 6 months and all is good.

[Mrmigs2011]

Replace the little seals on the map and tmap sensors too! Pinhole leaks on there gave my car a stumble,

Chargepipe seal likes nipping too so make sure it's well formed and intact.

I have to run my plugs at .8mm because of this very issue, still not beat it yet but getting close !

When I had a leaky injector I could see negative values lightly in stft, after replacing one idle fuel trim now sits at 0.

[Pito11213]

If you had leaky injectors and believe they were leaky for any significant amount of time, did you take a look at the injector port bores to make sure there are no issues there?

[suspect]

Originally Posted by AWD Addict

I know it's frustrating. I'd consider going with an mhd tune because of how robust the data logging features are.

I'm going to ngk one step colder plugs at my next service. My oe bosch plugs have about 10k miles on them (stage2+) and I'm hoping I can edge down IATs a bit with them. I've heard even BMW is using them now OE because the bosch weren't consistently good. I've heard a lot about gapping issues with the three prongers.

Consider a smoke test. It's a cheap way to eliminate leaks as part of the problem. Between that, checking for leaky injectora and minding your gas selection, you can cover a lot of area for low dollars first.

MHD and NGK are on the list now. What fuel do you use on stage2+?

I am looking at smoke tests now. It might be vacuum related as it changes with temperature. When I look from the side of the engine when the stumble happens you can see the engine slightly move.

[suspect]

Originally Posted by studio54

Yes, it's a fast test, pull AC ON, check your idle is at least at 800 rpm and let it idle one minute or two to see if it will still have a tiny one.

My bad, I also use 3 prongs Bosch (0242140507), I said 4 prongs because of the text I quoted that induced me to say something wrong. (I don't even know if there are 4 prongs plugs for the N54 ?!?)

Me too, next set, NGK (need to buy the gapping tool I guess...)

At 800 RPM the stumble is more consistent and happens more often.

No problem I am not sure if N54 ever had four prongs.

[suspect]

Originally Posted by E93Seattle (Racerbruce)

i too had an intermittent miss below 2k rpm's and while installing an aluminum chargepipe, bov, jb+ plug & play software, aluminum billet pcv i installed ngk iridium 2 step colder plugs and the intermittent idle disappeared; it's been nearly 6 months and all is good.

[suspect]

Originally Posted by Pito11213

If you had leaky injectors and believe they were leaky for any significant amount of time, did you take a look at the injector port bores to make sure there are no issues there?

The injector ports looked fine they did not look oval.

[suspect]

Originally Posted by Mrmigs2011

Replace the little seals on the map and tmap sensors too! Pinhole leaks on there gave my car a stumble,

Chargepipe seal likes nipping too so make sure it's well formed and intact.

I have to run my plugs at .8mm because of this very issue, still not beat it yet but getting close !

When I had a leaky injector I could see negative values lightly in stft, after replacing one idle fuel trim now sits at 0.

The tmap sensor is under the intake manifold isn’t it?

What were your LTFT like? My bank 2 LTFT constantly sits at negative. STFT is always changing but similar for both banks.

[AWD Addict]

Originally Posted by suspect

MHD and NGK are on the list now. What fuel do you use on stage2+?

I am looking at smoke tests now. It might be vacuum related as it changes with temperature. When I look from the side of the engine when the stumble happens you can see the engine slightly move.

I run 93 from any decent brand name. Most of the time it's fine. But there is definitely widely varying ethanol %, even among major brands. I'm not sure that's the issue, but the point is there's more variation in fuel quality than I think most people acknowledge. I think our finicky N54s are just hyper sensitive to that.

I had a tank of sumoco 93 a month ago, and my car idled like crap for most of it, and was pulling timing on my logs. Since I've been running the 91 octane map w 93 pump and have had no issues. Maybe I'm leaving a little push on the table, but she's still plenty fast for me.

[suspect]

Originally Posted by AWD Addict

I run 93 from any decent brand name. Most of the time it's fine. But there is definitely widely varying ethanol %, even among major brands. I'm not sure that's the issue, but the point is there's more variation in fuel quality than I think most people acknowledge. I think our finicky N54s are just hyper sensitive to that.

I had a tank of sumoco 93 a month ago, and my car idled like crap for most of it, and was pulling timing on my logs. Since I've been running the 91 octane map w 93 pump and have had no issues. Maybe I'm leaving a little push on the table, but she's still plenty fast for me.

I’m using 97-99 RON (93-94 octane) on a stock car and it runs like this. From reading I think 91 vs 93 can give or take 10-15 whp on a tuned car.

Is it possible to swap the pre cat o2 sensor wires between bank 1 and bank 2 considering one cable is shorter than the other? The LTFT on bank 2 is constantly negative so I wonder if switching between cables the bank 1 becomes constantly negative after driving then it would indicate bad o2 sensor.

[Mrmigs2011]

Originally Posted by suspect

The tmap sensor is under the intake manifold isn’t it?

What were your LTFT like? My bank 2 LTFT constantly sits at negative. STFT is always changing but similar for both banks.

Yep that's the one!


Ltft was slightly in the negative now only one is after switching out an injector suggesting to me I have one more problematic injector, I believe the ltft target 0 at wot if there are no real issues, then the stfts do all the on demand work.

Any hint of negative to my suggests some slight fuelling issues as the car shouldnt be pulling fuel.

I believe it is possible to get the wires mixed up so deffo make sure they're in the correct order.

There's a picture of the layout turbo side here for o2
https://www.e90post.com/forums/showthread.php?t=1848186

And here's my current log with faint stumbles but no missfire codes so you can compare.

https://datazap.me/u/mrmigs2011/mhd-stage-2-multi-config?log=0&data=3-21&solo=3&mark=35

[suspect]

Originally Posted by Mrmigs2011

Yep that's the one!


Ltft was slightly in the negative now only one is after switching out an injector suggesting to me I have one more problematic injector, I believe the ltft target 0 at wot if there are no real issues, then the stfts do all the on demand work.

Any hint of negative to my suggests some slight fuelling issues as the car shouldnt be pulling fuel.

I believe it is possible to get the wires mixed up so deffo make sure they're in the correct order.

There's a picture of the layout turbo side here for o2
https://www.e90post.com/forums/showthread.php?t=1848186

And here's my current log with faint stumbles but no missfire codes so you can compare.

https://datazap.me/u/mrmigs2011/mhd-...solo=3&mark=35

Thanks Mrmigs2011. I would expect LTFT to be pretty much zero like yours are. Do you have a log at idle (600-700rpm) too that you could upload?

[Mrmigs2011]

Originally Posted by suspect

Thanks Mrmigs2011. I would expect LTFT to be pretty much zero like yours are. Do you have a log at idle (600-700rpm) too that you could upload?

I'll get on that today for you, mine has been a little more stumbling again as of recent.

Another thing I've noticed is, try hold your revs at 1200-2000 rpm, go up in 100 rpm increments, my car won't hold a steady throttle at low revs and can hear the missing.

If I push the clutch in its even worse, I think that's starting to spool turbo lightly.

I can also hear wastegates (old and worn) not able to stick to one position.

Best idle I ever had was at 1.1mm spark gap, but too wide for this turbo engine for sure.

Another huge thing I've noticed,

Ambient temp...all the time is changing how often the stumbles are. In the rain more then the warm, something on the intake side perhaps, I need to pressure test the system again..

[studio54]

Originally Posted by suspect

At 800 RPM the stumble is more consistent and happens more often.

No problem I am not sure if N54 ever had four prongs.

Missed that message ! weird that higher rpm idling made things worst
On mine, higher idle equals less stumbles.

Do you have also stumbles when cruising at very low rpm (or outside idle) or just idle ?

No news?

To my understanding there aren't too many possibilities, I would guess it's either a plug not igniting correctly, either a leaking injector dripping one drip of fuel or something, resulting in a small pop/explosion in the exhaust for both scenario. Mrmigs2011 also said it could be a very small vacuum leak ? According my last measures, my idle inHg values seems normal and it appears too random to me to be a vacuum leak.

I also need to figure that on mine and since I have to change plugs, I will start by this in november, I will also check at the same time if one or some of the old ones are wet cause thoses small stumbles (+ natural burbles on let off but I have the PE exhaust) always made be believed I've had a slight leaky injector since I have this car.