[DLucian]

Greetings everybody,

I am trying to diagnose a fault with my automatic N55 - 335i E91.

Basically, when the car is in drive and I let off the brake without touching the gas, the car will start to violently jerk forward and fluctuate the idle RPM's as in a really rough idle situation. This only happens if either the steering is close to max lock in either directions or if I partially disengage the brake pedal. If the A/C is on, it's worse. If A/C is off, steering is straight and I fully disengage the brake, 99.99% of times it doesn't happen.

When a friend of mine had the car, he told me that the engine actually died on him once when this happened. He just let go of the break paddle with maximum steering lock, in drive, idle started fluctuating and engine died.

Sometimes, when coming to a stop while turning the wheel, this also happens and I have to really stomp on the brake to make it stop (almost crashed into another car at one point). Again, it fluctuates before stopping and when rpm's increase, I have to push harder into the break pedal as it pulls the car more.

This leads me to believe that something that is controlling the idle is failing somehow or something is causing excessive load. Maybe also something gearbox related? Shifting feels fine to me. Also had a fluid change and this behaviour did not change.

I replaced the steering pump, thinking that it might cause excessive drag. This helped a little but not much. Also refreshed all vacuum lines but to no avail.

I have no fault codes and besides this, car runs and drives fine.

Any ideas would be greatly appreciated. Thanks!

[Yotaismygame]

Sounds like Vanos solenoids.

https://bmwtuning.co/diagnosing-a-fa...-vanos-system/

what mileage is on the car?

[DLucian]

Thanks for the reply. Car has ~110k miles.

Looking over the link, given the symptoms, I am guessing the best thing would be to clean the solenoids. Right?

It seems fairly easy. Will do this regardless and report back.

Thanks again.

[witty]

def Vanos solenoids, this had happened to my car, sprayed some break cleaner and got much better, remember there's a gasket don't lose it.

[Yotaismygame]

Originally Posted by DLucian

Thanks for the reply. Car has ~110k miles.

Looking over the link, given the symptoms, I am guessing the best thing would be to clean the solenoids. Right?

It seems fairly easy. Will do this regardless and report back.

Thanks again.

At that mileage and if original I would definitely replace them if you're going to be pulling them out. My brothers n55 only has 65k on it and his need replaced already.

[DLucian]

Status update, I pulled out and cleaned the solenoids and the car feels... worse than before. It does it more often and now the idle is rough where it was not before.

Stupidly, I forgot to test resistance and I hate myself for this. On the other hand, now I am deeply inclined to believe that this is the source of my problems so, at least I may have found the issue.

This brings me on to my next problem. I want to replace them both. Over here in Europe, I have a good supplier for aftermarket Pierburg or VDO that are half the price of BMW ones. Also, the BMW ones arrive in 1 week or more and the aftermarket ones in 2 days and I was hoping to fix it before my trip over the next weekend. Given this, I am really tempted to go with Pierburg as I know they make lots of BMW parts but I am seeing mixed opinions on this.

Any ideas or thoughts on this would be helpful. Thanks!

[Yotaismygame]

Originally Posted by DLucian

Status update, I pulled out and cleaned the solenoids and the car feels... worse than before. It does it more often and now the idle is rough where it was not before.

Stupidly, I forgot to test resistance and I hate myself for this. On the other hand, now I am deeply inclined to believe that this is the source of my problems so, at least I may have found the issue.

This brings me on to my next problem. I want to replace them both. Over here in Europe, I have a good supplier for aftermarket Pierburg or VDO that are half the price of BMW ones. Also, the BMW ones arrive in 1 week or more and the aftermarket ones in 2 days and I was hoping to fix it before my trip over the next weekend. Given this, I am really tempted to go with Pierburg as I know they make lots of BMW parts but I am seeing mixed opinions on this.

Any ideas or thoughts on this would be helpful. Thanks!

Just use the Pierburg.

[DLucian]

Updates: Changed the solenoids , used OE ones just because I wanted to clearly eliminate this being a potential issue, and it did not fix it.

I am tempted to say it has improved and it is not doing this as often right now, but unsure at this point if it is simply placebo or an actual improvement.

I did this in a bit of a rush and did not have time yet again to test the old solenoids for resistance or check the date on them to see if they were ever changed.

Anyway. This still bothers me although, at this point, I am not feeling like throwing more money at this evidently small issue and I am considering leaving it as such until something actually happens or any of you guys have a concrete idea how I can test something and replace if I know the part is broken.

One more thing I would be considering is HPFP. This is the first gen N55 that had the more unreliable design. I have no evidence of it ever being changed and I know it is prawn to failure so I am considering changing it as a preventive maintenance thing. Any ideas on this? Is there any live data I can check with ISTA to see if the HPFP is within working parameters? Maybe when this jerking happens, the pressure fluctuates in a way that it shouldn't? HPFP failure is usually just misfiring / no start type issues or could it be this? Car runs and pulls perfectly and has been having this "jerking" symptom since I bought it, about 5k miles. This, in a way, tells me that if it was a HPFP thing, it would have totally failed by now.

Thanks again for all of your help.

[Mdilo]

Originally Posted by DLucian

Updates: Changed the solenoids , used OE ones just because I wanted to clearly eliminate this being a potential issue, and it did not fix it.

I am tempted to say it has improved and it is not doing this as often right now, but unsure at this point if it is simply placebo or an actual improvement.

I did this in a bit of a rush and did not have time yet again to test the old solenoids for resistance or check the date on them to see if they were ever changed.

Anyway. This still bothers me although, at this point, I am not feeling like throwing more money at this evidently small issue and I am considering leaving it as such until something actually happens or any of you guys have a concrete idea how I can test something and replace if I know the part is broken.

One more thing I would be considering is HPFP. This is the first gen N55 that had the more unreliable design. I have no evidence of it ever being changed and I know it is prawn to failure so I am considering changing it as a preventive maintenance thing. Any ideas on this? Is there any live data I can check with ISTA to see if the HPFP is within working parameters? Maybe when this jerking happens, the pressure fluctuates in a way that it shouldn't? HPFP failure is usually just misfiring / no start type issues or could it be this? Car runs and pulls perfectly and has been having this "jerking" symptom since I bought it, about 5k miles. This, in a way, tells me that if it was a HPFP thing, it would have totally failed by now.

Thanks again for all of your help.

Any luck figuring this out?

[Bimmere90n55]

Mine does this as well and I also have no active faults. Just went through basically the whole used motor before swapping it in with 65k on it. Put about a thousand miles on it now and I've noticed the same thing happening. No active codes, only the shadow code of the hpfp pressure too low. I'm wondering if that is the cause as well. I'm not sure what psi the rail pressure is suppose to be. I also have the squealing from either the front and/or rear main seal going out 🙄. Unsure if any of those factors are playing a part in it.

[Mdilo]

You should definitely fix the squealing asap. If it’s your pcv then your crankcase pressure could be too high causing a bunch of issues.

[DLucian]

Some updates but no good news. At this point I simply got used to the car as it is. Issue is still present, around 30k km later.

I am pretty sure it's not fuel pressure related. If it was that, I believe in 30k km it would have failed by now.

I don't think I said it before but, ISTA has a feature where you can input some issues of the car (things that you can see or feel) and, in combination with error codes, if any, it will suggest what to do. I did this and it suggested getting a newer I Level, a software update, basically.

Now, this sounds simple but my car has lots of retrofits and also a working official BMW Performance power kit from the previous owner. I went around to lots of dealers and none could confirm that the power kit or that my retrofits will not be affected in any way by the I level update.

So, currently, I feel really stuck with this, unfortunately.