Rough idle or not? help please...

[ForZ4]

My '14 35is (3mo new to me) seems to have a slight rough idle, typically noticeable when A/C is off (seems to smooth out when AC is on due to higher rev idle). It's not really rough, but just like slightly percolating that can be felt on the seat of my pants. Is this normal? Otherwise it drives fine, however, it does seem to smell of fuel when idling in a semi-confined space, i.e.: a car port... but this just might be my imagination.

I've mentioned this to the dealer during my 15k oil service, they checked the codes and said none given and everything seems fine. Now this may be the case, as my only experience with an inline 6 was my old 88 toyota supra turbo which when idling seemed as if the car was off, it was that smooth (and interior sound proofed). Now I know these are two different types of cars, however I'm not sure if this is an issue or not.

Also, now this may be way off base to determine anything, but when I place my hand near the Driver Side/Pass Side tail pipes, it seems the DS has much more "air" coming out from it vs. the PS. But I know the vacuum control / exhaust valve is on the PS - would this mute the "air" pressure (by feel) somewhat? Told my service tech that and he said that the "other" exhaust is "more like cosmetic"... now this isn't the case, right? Correct me if I'm wrong but the 35i(s) are fully isolated dual mirrored exhausts, right?... except for the exhaust valve.

This slight roughness in idle is not really a bother -if it is indeed operating normally perhaps like a typical roadster, but I'm just concerned something may be amiss and obviously would like it addressed.

I have a service appt on monday and would like to go in with more knowledge. I appreciate any feedback.

[Asbjorn]

Mine has the fuel smell as well. No idea where it is originating from. Hope others can help.

The exhaust is a true dual one. I wouldnt worry about the exhaust air flow at all.

The car *should* be smooth at idle. AC on or off. But after mine passed the 50k km mark, and only with AC off, it sometimes has a hiccup where rpm increases like +50rpm. Not much but can be felt. Happens maybe once every second minute. Rest of the time it is butter smooth.

[nicknaz]

Keep an eye out for the rough idle. My '12 35i had a rough idle that turned into a long crank and in the end injectors and hpfp got replaced.

Should be a resolved issue by now so you should be ok if there are no codes

[CedarZ4]

I've been having rough idle for the past year now and like OP, no codes or issues from the dealership either.

Recently I've had rough starts on top of that and they finally replaced 2 of my injectors. That fixed the long crank issue, but idle still shakes the car (I can see the water in my water bottle shaking pretty violently). No HPFP issue on my side so far (knock on wood) but Nick's suggestion on having the injectors checked may be be a good start, as those two seem to be the main problems coming up on the E89 after 6 years of production.

[tranquility]

Originally Posted by CedarZ4

I've been having rough idle for the past year now and like OP, no codes or issues from the dealership either.

Recently I've had rough starts on top of that and they finally replaced 2 of my injectors. That fixed the long crank issue, but idle still shakes the car (I can see the water in my water bottle shaking pretty violently). No HPFP issue on my side so far (knock on wood) but Nick's suggestion on having the injectors checked may be be a good start, as those two seem to be the main problems coming up on the E89 after 6 years of production.

Why did they only replace 2? If you're under warranty, you should tell them to replace all.

[ForZ4]

Guys - thanks for all the info... please elaborate on anything else that might be pertinent to this as this is really helpful to me.

Also, I should mention after seeing nicknaz & CedarZ4 mention "long crank issue", I googled it and found out sure enough... this has happened to me twice within the last couple of weeks or so. I did mention this to the dealer, but of course they told me they could not recreate and no codes were thrown.

So it sounds like there might be a potential hpfp issue or injectors ?? I thought BMW had this worked out already as this is a MY 2014. I am routinely videoing my start-ups to try and catch it in the act & have data for the dealer.

Another question - so the typical idle rev with AC off is at 650rpm, yes? Today everything seems smooth, but I noticed idle is nearer to 750rpm and the AC is off - strange? fwiw - it is a cooler low 70s weather if that means anything.

Anyway, I appreciate any and all comments. Thanks!

[tranquility]

My idle is ~550rpms regardless of AC on/off. Our engines can handle the AC w/o feeling burdened, unlike the 4-banger in the Audi TTS, for example.

Long cranking and 'violent' shaking are symptoms of a bad hpfp and/or fuel injectors. I6 is supposed to be freaking smooth, that's one of its trademarks, so if you're experiencing these things, there is definitely something wrong w/ it. Surprised that it didn't throw some codes and the dealer couldn't figure out what's up. GL.

[CedarZ4]

When they told me they were replacing injectors, I was expecting them to replace all 6 a well. When I went to pick up the car though, they told me just the 2 faulty ones were replaced. Maybe next service I'll have them peak in there again.

Back on topic. Like OPs, I idle at around 650rpm as well and another 100 when AC is on. That seems to be normal. There are days (but very rarely) where it WILL stay idled at 750, even 850, without the AC on. This seems to happen more often after driving very spiritedly as well, even after cool-down "lap". Were you WOT prior to it idling higher?

Also, since your car is new and has plenty of warranty left, I wouldn't bother trying to "recreate" the problem. Soon or later, most likely the former, the CEL will show up like mine did. Not the best approach, but what can you do. My dealer said they couldn't find any problem on mine either when I brought it in the first time for rough idling.

[nicknaz]

OP, I think Cedar is right and you should just enjoy your car for now and just keep an eye on it. at some point if it worsens long crank will get very repeatable and it will be very clear at that point.

by the way, is your car leased? if so, maybe you can do an easy DIY and try an "italian tune up"

I have been doing those a lot for the last 3 years and hopefully I've helped to save a future CPO buyer from a "walnut blasting" and shaken down the car for other issues

[ForZ4]

Well quick update after dropping the Z at the dealer - they told me they found injectors needing replacement. They are keeping it one more day as they still have some other items they want to "check and finish up". Will update as I find out more.

I've perused the net and found others having injector issues on the N54, but none I saw on this late of a MY... I guess they leak and somewhat flood the cylinder at rest - thus the long cranks and the fuel smell on start-up. Someone even mentioned the leaking injector contaminated their oil causing additional problems- from their logic.

to answer some of your questions:

Originally Posted by CedarZ4

Were you WOT prior to it idling higher?

maybe a little spirited, but WOT - not ever for a long duration - just for a quick moment if at all.

Originally Posted by nicknaz

by the way, is your car leased?

nope - CPO dealer purchased used w11k miles

Anyways - Thanks again guys for all the info and help!

[HerrK]

Took the Z in to dealer today for cold start rough idle, misfiring, & CEL illuminated. 6 fuel injectors replaced on the N54 @ 35K miles. Thank goodness for the extended warranty. Counting parts @ $1500 and labor I've got over half of the 7 yr extended warranty purchase recouped.

[SpikeMilligan]

My 2012 started having rough idle and long cranks about a year ago. After several months it ran really rough after starting one time and threw some codes. They replaced all the fuel injectors under warranty. I now make sure to use fuel injector cleaner in the gas regularly (not their suggestion), and the mechanic suggested that I am driving the car too easily, it needs some quick acceleration sometimes to blow out the carbon. I also try to use Shell V-Tec gas since a lot of people on these boards seem to recommend it - but it's sometimes hard to find on a road trip.

[sjeupie]

I only just learned about this issue in this topic. Here everybody has the 35i(s). Should I be aware of it as well with my 23i my2010?

[Lurcher]

Don't forget since these engines are direct injected, carbon/gunk buildup around the valves is a major issue. Plenty of info on the web about walnut blasting, even as early as 30k miles....