[pjb515]

2007 E90 automatic N5x engine
I'm not sure you'd call this rough idle, it's really an RPM dip but wasn't happening if in neutral so is it the transmission? The issue:
For a few weeks now while stopped and in Drive, such as sitting at a red light, RPM's "Blip" down from 600 to 500 and immediately go back to 600. The time it takes to say "Blip" is how fast it does this little dip. RPM's never go up above 600 or below 500, only this very quick dip to 500 and back. Frequency varies a bit but if sitting for a full cycle at a red light it's going to do it several times. Seems to not do it at first when stopped but maybe after 30 seconds it'll do it for the first time then potentially every few seconds but not guaranteed.

-Doesn't matter if the engine is hot or cold
-I swear it wasn't doing it when in neutral but concentrating on the behavior today in preparation of writing this post, it does it in neutral too.

So far I've cleaned the vanos solenoid (Using carb medic choke and valve cleaner) and the MAF sensor (Using CRC MAF cleaner). I've gone through at least one full tank of 93 top tier fuel, and for the record I've only put 93 in it just not always top tier. After more research it seems like I should also clean the other solenoid thing directly below the vanos but I'm not sure... I have a Bavarian Technic OBD tool so in the morning I'll see if that tells me anything I can understand.
I'm no mechanic so maybe time to get it looked at but the purpose of this post is mostly to ask if you think it's an idle issue or a transmission issue. Seems to me if it's engine-related it would act the same no matter which gear it's in, correct? It truly was non-existent in neutral before today, I swear!

[M.chowdhury1]

I'm also having the same issue on my 320i 2007.... funny thing is, i just got a full service done the morning before it started to happen

[pjb515]

New behavior and error code:
Going up an inclined straight highway onramp today, car ran rough and stuttery as it tried hard acceleration up the onramp and also got the "Service engine soon" warning lamp. After leveling out the warning went off. I drove straight home and did get another momentary warning lamp, same one, by the way not to be confused with the check engine lamp, that's a different one and didn't light up.
Error code was a 29D1 misfirings, cylinder 5. Gonna try just a spark plug ($29 each!) and hopefully get lucky. I'll update when I have news but I figured I'd post these events and maybe someone would chime in their thoughts.

[skyview]

I literally haven't logged into this account in over 4 years, but I am occasionally on these forums doing research on something that's come up with my car. Normally though, they're all old common problems with these cars which many other people have already answered or assisted with. However in this particular case, I stumbled on your post today and was actually excited to see that I've had the same exact problem as you're having and that no one has replied...yet!! So I was pretty psyched to go and click "reset password" in order to be able to log in and share with you my experiences, and hopefully give back some help as this forum has certainly helped me a ton over the years!

Now that I got that out of the way haha... I've actually had the same symptoms you're describing come up twice on my 2008 328xi. First time was about 5 years ago and then it also happened again a year ago. The first time, the dealer replaced the ignition coils and cleaned the spark plugs and everything went back to normal (covered under extended warranty). The second time, the dealer replaced the ignition coils, spark plugs, and fuel pump and that fixed the issue (covered under SULEV warranty). The car was also throwing cylinder misfire codes as you mentioned.

Even though the dealer replaced the fuel pump the second time I had this issue, I'm not positive whether it was necessarily related. While it might be, I would probably put my money on the ignition coils being at fault first, since I did replace all spark plugs a few years ago so they actually weren't that old. I'm not sure why the coils went out so frequently though, especially considering that my car only has 75k miles.

@pjb515-- I see you're in Massachusetts. I believe Massachusetts is included under the SULEV 15 year/150k mile warranty, if your 328i has the N51 engine and you're under 150k miles.

[PassiveDefect]

sounds like a HPFP

[pjb515]

I got so lucky, turned out to be just a spark plug! After getting that error I googled and found different info/fixes. One of them was a guy that had posted the same error code and tried just a spark plug first and it fixed it for him so being cheap, I tried that too before buying coils etc. I didn't mess around and bought one from the stealership, $27 US! I've bought spark plugs before, and paid just a buck or two... anyway that took care of it. If you end up doing the same, note that it may not seem resolved immediately. I started driving the car and it seemed great but it did it again a few times. I don't know how many miles I had put on the car during that first period, let's say at least 5? Initially I didn't have the problem but then I noticed a couple of those dips. I went back home and hooked up the scan tool, the error did not come back. I've been driving all day now (Uber), and it's been fine. It's a mystery that it did it at all after putting the new plug in, seems to me that's not the type of problem that needs to "Adjust". If you end up doing the same, check youtube for videos on accessing the plugs/coils, you'll want to pay close attention to the part where they show you how to dislodge the wire harness from the air filter tray. I had trouble dislodging mine and had to watch a couple different videos to piece together how to do it without breaking anything. There's a lot of cheap plastic there so be patient and careful or you're sure to break something.
Thanks for your input, everyone!

[alexg212]

Originally Posted by pjb515

I got so lucky, turned out to be just a spark plug! After getting that error I googled and found different info/fixes. One of them was a guy that had posted the same error code and tried just a spark plug first and it fixed it for him so being cheap, I tried that too before buying coils etc. I didn't mess around and bought one from the stealership, $27 US! I've bought spark plugs before, and paid just a buck or two... anyway that took care of it. If you end up doing the same, note that it may not seem resolved immediately. I started driving the car and it seemed great but it did it again a few times. I don't know how many miles I had put on the car during that first period, let's say at least 5? Initially I didn't have the problem but then I noticed a couple of those dips. I went back home and hooked up the scan tool, the error did not come back. I've been driving all day now (Uber), and it's been fine. It's a mystery that it did it at all after putting the new plug in, seems to me that's not the type of problem that needs to "Adjust". If you end up doing the same, check youtube for videos on accessing the plugs/coils, you'll want to pay close attention to the part where they show you how to dislodge the wire harness from the air filter tray. I had trouble dislodging mine and had to watch a couple different videos to piece together how to do it without breaking anything. There's a lot of cheap plastic there so be patient and careful or you're sure to break something.
Thanks for your input, everyone!

You could have bought the same oem Bosch plugs for a few bucks each. I paid not even $50 for all six last time I ordered some.

[pjb515]

Originally Posted by alexg212

You could have bought the same oem Bosch plugs for a few bucks each. I paid not even $50 for all six last time I ordered some.

I thought of that but this was one of those "Just in case" things so I spent the extra money to be sure I didn't cause any new issue. I really knew I could get another plug but didn't know which one would be a good reliable one and definitely can not afford to have an additional thing to fix so I bought the oem "just in case". I assume if I were to post the question of which plugs I should buy, I'd get a full range of opinions, which only overwhelms me...

[alexg212]

Originally Posted by pjb515

I thought of that but this was one of those "Just in case" things so I spent the extra money to be sure I didn't cause any new issue. I really knew I could get another plug but didn't know which one would be a good reliable one and definitely can not afford to have an additional thing to fix so I bought the oem "just in case". I assume if I were to post the question of which plugs I should buy, I'd get a full range of opinions, which only overwhelms me...

Just stick with the oem Bosch. Maybe colder NGK 5992. Most run stock just fine.