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-   -   N55 owners, idle not smooth? (http://www.bimmerfest.com/forums/showthread.php?t=572965)

thekurgan 10-05-2011 07:02 AM

N55 owners, idle not smooth?
 
I recently had my car in for service and wound up leaving it two days and had two different loaners. The first was an F10 535i, which was nice to test drive, so we could eliminate it from our choices of a replacement car :) The other was a 135i with DCT. Little thing was a rocket FWIW and the DCT was very smooth. What I noticed with both vehicles was the idle was not smooth, it was "lopey" and I wondered if this was the norm for the N55 or if maybe since we've recently read some idle issues with the N52, is it valvetronic causing the idle issues? I don't have enough knowledge with respect to how valvetronic works, but it almost feels like my S54 on very cold days, before the valves get to stretch a bit (30 seconds).

Just thought I'd throw it out there, it is possible there were issues with both loaners, both had in excess of 12k miles and maybe just needed some techron, or maybe previous drivers failed to use 91 octane fuel.

Ilovemycar 01-19-2012 01:40 PM

Hi kurgan, forgive the necrobump, and that I have a N54. After doing a title search for "idle" in this subforum, so far your thread is as pertinent as any, if I understand the "lopey" right. Much of my driving, I think the idle is smooth at say 600. However, on occasion it starts oscillating between 600 and 700 (I've tried to "time" the oscillation in my head, but if I had to guess, it's not a consistent speed always, so to speak). Last night when stopped at a very mild incline, it was at 600 went up to 700 where I expected an oscillation, and instead climbed right up to 800 and stayed there.

Is this all "normal", maybe dependent on temperature too? I only use 91, and every tank except one during my ownership has been Chevron or Shell, and I've probably used Techron (one bottle only) before every annual oil change. If this is just normal, I can ignore it easily enough, but if it's something that may require attention, I'd like to know more. Thanks.

Sometimes when it "oscillates" at a stop, I'll just blip the throttle with my heel, and it's smooth again. :dunno: Maybe what I'm describing has little/nothing to do with what you're talking about?

OK, I have a bonus question for you, since I have your ear. Recently, I feel like the tranny hesitates a little more before "catching" sometimes. I'm almost positive I never felt this until I got new tires a few months ago. I'm sure it's probably just the driver and his technique here, because I have an almost impossible time thinking tires could affect this (outside of maybe some huge diameter/tread change, but even then . . .). Thanks for listening.

Verts4Ever 01-19-2012 02:34 PM

Quote:

Originally Posted by thekurgan (Post 6360170)
What I noticed with both vehicles was the idle was not smooth, it was "lopey" and I wondered if this was the norm for the N55 or if maybe since we've recently read some idle issues with the N52, is it valvetronic causing the idle issues?

That happens occasionally on ours when just started and the ambient temp is on the cold side (I'd say below 20 F), but it's very mild and my wife doesn't even notice it.

I've been wondering if it's not due to the wastegate oscillating to compensate for the turbo doing so while warming up and creating a minor positive feedback loop, but the valvetronic could easily be the issue too. Either way, I'd think it would be a simple fix via a DME update.

Or it could be something else entirely that will become the HPFP issue for the N55. :)

SteVTEC 01-19-2012 06:11 PM

Sometimes, on cold starts only, the RPMs will oscillate a bit as if the throttle is being blipped on my N55. Can go above 1000rpm while 'blipping'. No check engine or warning lights, but I've felt/detected a misfire on some of these cold starts. I think this is normal since others with N55's have reported similar behavior, and that this is BMW's way of dealing with some of the challenges that cold starts with direct injection presents. Audis have had similar issues, I think. On the Lexus 'dual injection' engines that have both port and direct injection (2GR-FSE, 3.5L DOHC, 306hp IS350, GS350, etc), they actually run 100% port injection on cold starts to get around this. It also fixes the intake port deposit issues that pure DI engines have. I think the blipping allows it to run a slightly higher idle load which gets around the issue. When it does this, which is not all the time, it purrs like a kitten with a nice smooth idle after 10-15 seconds.

gcreese 01-20-2012 05:08 AM

On my 2011 335i xDrive, the idle will be all over the place when I initially start it. However, once I start driving the car it goes away.

DSXMachina 01-20-2012 05:33 AM

It's extremely difficult for the Powertrain Control Module (PCM, also called the main computer, the ECU, the ECM and a few other tems) to control a cold engine within a very narrow rpm band, it gets easier as it warms up. Valvetronic stuff should have nothing to do with loping idle speed, everything is at 'zero' in the mechanism until load or rpm changes.
When a cold engine starts is when the most pollutants occur. More emissions happen during the first five minutes than in the next couple hours. The PCM has to consult the intake air temperature graphs, the intake air density graphs, the engine temperature graphs, the fuel octane and composition (methanol percentage?) graphs, the barometric pressure graphs, the accelerator pedal position graphs, the injector history graphs, the long term fuel trim graphs and whether the driver is drinking coffee graphs. It then tries to come up with an injector pulse which will nail the desired rpm while doing a delicate balancing act with the idle air control bypass system. It ain't easy.
Most often the 'problem' is software related and mfrs. do a recall to tweak the algorithms once they get enough field information. What takes forever is getting the EPA to certify these tweaks before they're released, they want to make sure that the car will still meet emission standards after the new software is installed (often called 'reflashing').

thekurgan 01-20-2012 07:38 AM

I experienced this unsmooth idle when the vehicles were warm, felt like an old school vacuum leak. N54 vehicles were extremely smooth at idle.

Problemeveryday 01-20-2012 11:11 AM

idle issue
 
i have a N55 MT coupe with every single add on possible. when you turn on the car regardless if its cold start or not, the RPM will be above 1k for sure. What happens is your radiator, and intercoolers shut down when the car is off so it needs to warm up when you turn the car on. and that takes about 15-25 seconds. I always listen to my cars engine because i already know by hear when its ready to leave the garage. you never want to take out a car right away when you turn it on. those rent cars you are talking about........people drive those like go cars. so did i to be honest i had a 335i sedan diesel as a loaner and i drove the **** out of it lol. So heres an example, if you open your eyes in the morning can you run the marathon? no. so when people turn on their cars, most dont wait for the RPM to rest before taking off. even if your leasing the car, it does not mean you need to **** it up because you might be able to purchase it for a great deal. the best car investment is financing a car that you have been the only owner and you know yourself that the car has got no problems. I have owned a BMW since 2001 a e46 330i, 330i zhp, m3, and currently a N55 335i MT.


As far as gasoline, i have put nothing but MOBIL 91 in all my cars since 01 except maybe once or twice chevron or shell. if you keep up with the stats MOBIL won the highest rating for gas recently. I never let the dealer change my oil i have done it myself.

Ilovemycar 01-20-2012 08:05 PM

For the first time ever, I attempted a quasi Italian tune-up today. I tried searching to see if people had suggestions for gears/RPMs/time, but anyway I drove about 25 miles, about 20 of those being faster miles, most of which was probably in 3rd. I kept it mostly in the 4500-5000k ballpark, and never really redlined it (I would be afraid of longer term redlining, or even 6k for an extended time, just being careful I guess.) Idle is extremely smooth again, we'll see if this remains true. I'm going to make a point of doing this a little more often. I'm out of Techron, and I'll order more shortly before my next oil change. Do you guys find it perfectly fine to use the fuel system cleaner even when the oil change won't be for a while, or is it just best to wait? Oh, I'll also gladly take pointers for my next I.T.U. Thanks.

DSXMachina 01-21-2012 07:16 AM

You want a professional opinion? Techron is good stuff, use it myself and have 'cured' many customers' engines' hiccups. That doesn't make it a good long term additive. Just as taking a medication should stop when the illness is over, stop with the Techron when either the fix is accomplished or it didn't work.
It's powerful chemistry and I'd be very leery of chronic use. Buy good gasoline instead.

thekurgan 01-21-2012 07:55 AM

Quote:

Originally Posted by DSXMachina (Post 6577327)
You want a professional opinion? Techron is good stuff, use it myself and have 'cured' many customers' engines' hiccups. That doesn't make it a good long term additive. Just as taking a medication should stop when the illness is over, stop with the Techron when either the fix is accomplished or it didn't work.
It's powerful chemistry and I'd be very leery of chronic use. Buy good gasoline instead.

Completely agree, a great once-in-a-while product.

Ilovemycar 01-21-2012 10:29 AM

DSX, your pro opinion is always appreciated, thank you. Just in case it wasn't totally clear, I didn't use Techron yesterday, as I already had none left for a while now. The most often it's ever been used is once a year right before an oil change, and good gas is basically the law with my car. :thumbup: Heck, I used to make sure any loaner car I received got good gas. :D

westwest888 01-21-2012 12:13 PM

Quote:

Originally Posted by thekurgan (Post 6360170)
I recently had my car in for service and wound up leaving it two days and had two different loaners. The first was an F10 535i, which was nice to test drive, so we could eliminate it from our choices of a replacement car :) The other was a 135i with DCT. Little thing was a rocket FWIW and the DCT was very smooth. What I noticed with both vehicles was the idle was not smooth, it was "lopey" and I wondered if this was the norm for the N55 or if maybe since we've recently read some idle issues with the N52, is it valvetronic causing the idle issues? I don't have enough knowledge with respect to how valvetronic works, but it almost feels like my S54 on very cold days, before the valves get to stretch a bit (30 seconds).

Just thought I'd throw it out there, it is possible there were issues with both loaners, both had in excess of 12k miles and maybe just needed some techron, or maybe previous drivers failed to use 91 octane fuel.

I was reading the article in Motor Trend or C&D this month where they take the cars around VIR's grand course (4.6 miles or something crazy). Surprisingly, the 335i with DCT transmission did horribly (slower than a manual 335i tested a few years back). Something about the shifts sticking and them blowing several corners because of it. They couldn't wring a good lap out of it. Is that transmission literally the same part number as the one for the M3, or a "me too" version with different software and friction points?

Verts4Ever 01-21-2012 12:58 PM

Quote:

Originally Posted by DSXMachina (Post 6574992)
The PCM has to consult the intake air temperature graphs, the intake air density graphs, the engine temperature graphs, the fuel octane and composition (methanol percentage?) graphs, the barometric pressure graphs, the accelerator pedal position graphs, the injector history graphs, the long term fuel trim graphs and whether the driver is drinking coffee graphs. It then tries to come up with an injector pulse which will nail the desired rpm while doing a delicate balancing act with the idle air control bypass system. It ain't easy.

Thanks, DSX. Very informative stuff.

thekurgan 01-21-2012 04:02 PM

Quote:

Originally Posted by westwest888 (Post 6577851)
I was reading the article in Motor Trend or C&D this month where they take the cars around VIR's grand course (4.6 miles or something crazy). Surprisingly, the 335i with DCT transmission did horribly (slower than a manual 335i tested a few years back). Something about the shifts sticking and them blowing several corners because of it. They couldn't wring a good lap out of it. Is that transmission literally the same part number as the one for the M3, or a "me too" version with different software and friction points?

I believe the M3 DCT is rated differently and would be a different part number. I can check penskeparts or realoem, but I do remember reading that they were different units. There are already upgraded parts for these DCT units; I remember seeing an article in Roundel with a supercharged DCT unit had upgraded parts.


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