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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Steady throttle low rpm issue



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      11-16-2011, 07:19 PM   #1
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Steady throttle low rpm issue

For quite some time now i have been experiencing a weird issue.
At steady throttle around 2000 rpm mostly on high gears the engine kind of accellerates by itself 100 rpm and goes back in a wave like motion.
I can see the negative boost pressure going from like minus 18 to minus 12 or so .
This happens on procede, cobb and stock. i thought it could have been related to injectors but those are all new now. All lambdas are new as well as spark plugs.
I also thought the AT transmission was the cause but i have rebuilt it.
I think it pretty much started to notice this after the engine was rebuilt. Not sure though .
The head is also ported.
What do you think it could be?
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      11-16-2011, 07:27 PM   #2
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I have this issue as well since the car was new. It does it with and without tune but is more noticeable with tune in my opinion. I took my tune out several years ago for a dealer visit and took a tech for a ride to show him, because it is very easy to see on the Rixter gauge as you mentioned. He said this was normal and that it was the ECU minutely adjusting fuel flow at low rpm and load. If I concentrate on it I notice it, if I am jamming to music I don't, so I just gave up on any fix as it seems to be prevalent on the N54.
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      11-16-2011, 07:40 PM   #3
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I think this may due with how DME charges the intake pre-throttle. n54 has a fairly high pressure differential across the throttle and discharges it through the DVs... much of this depends on your WG default position I would think. I believe I have felt this in lower gears, mainly when cold... but cruising in the higher gears never noticed.
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      11-17-2011, 02:52 AM   #4
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ok guys thanks. At least i am not the only one with this issue. I thought it could be something "head related" . is quite noticeable on my car, you really feel the push forward and back and yes more so the colder it gets (i live in sweden so very cold) .
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      11-17-2011, 02:54 AM   #5
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I wonder if it has anything to do with the stratification mode that the DME goes into when cruising?
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      11-17-2011, 03:15 AM   #6
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maybe? gonna read more on this stratified.
my software got updated end of october 2010 (Car is MY march 2007) . can those with the same issue state their car ECU software? or just year/month when it got updated ?
Could be this issue started after the update.
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      11-17-2011, 12:11 PM   #7
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Supposedly n54 does NOT have stratified charge... at least in the US, but I think overall. This is due to inconsistencies in gasoline. In the US sulfur content is way too high which produces excessive NOx. I also heard that the injector solenoids do not have the ability, as strat mode requires a very small window of injection. The pistons also don't seem to be constructed like other stratified charge engines.

May have a lean burn mode though, but this is basically homogeneous during the intake stroke. anyway...
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      11-17-2011, 12:23 PM   #8
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I got more reports on an italian forum. Same issue there as well from some people. Exactly the same behaviour. Also on the BMW software revisions and versions they write about this "revised lean burn" cruising mode.
I am more inclined now to believe its BMW software related and that this came up when i updated it in october 2010.
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      11-17-2011, 12:27 PM   #9
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I have a feeling its is the new software that geared towards the go green ideology to produce less and use less gas. I have never felt this issue you guys describe with my car.
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      11-17-2011, 10:56 PM   #10
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Quote:
Originally Posted by cn555ic View Post
I have a feeling its is the new software that geared towards the go green ideology to produce less and use less gas. I have never felt this issue you guys describe with my car.
Maybe the latest MSD80/81 software is causing their problems. You said you have specifically not updated your ECU in a long time, right?

I checked mine on the Autologic, and it said everything was up to date, but I had to connect the WiFi to check for ECU updates (PITA). So I just left it alone. I also do not experience any of that phenomenon, early 07/2006 build US car. I just got it used at Carmax in Sept, and it appeared to be very well maintained. I guess if they didn't take it to the dealer for maintenance, then it would not have been updated to the 29.x software that I suspect may be partially to blame for this.
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      11-17-2011, 11:04 PM   #11
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Quote:
Originally Posted by JamesM3M5 View Post
Maybe the latest MSD80/81 software is causing their problems. You said you have specifically not updated your ECU in a long time, right?

I checked mine on the Autologic, and it said everything was up to date, but I had to connect the WiFi to check for ECU updates (PITA). So I just left it alone. I also do not experience any of that phenomenon, early 07/2006 build US car. I just got it used at Carmax in Sept, and it appeared to be very well maintained. I guess if they didn't take it to the dealer for maintenance, then it would not have been updated to the 29.x software that I suspect may be partially to blame for this.
The software version is way beyond 29.xx! I have no idea what the latest and greatest BMW has come up with now!
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      11-18-2011, 12:45 AM   #12
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I have had the same symptom from the original version 25, through the current version which was done on fuel pump recall about 6 months ago, with several updates in between. The symptom I feel is most noticeable on a flat road with cruise on, at about 2000 rpm. When you get to a point where there is hardly much of a load and you are getting about 28-30 mpg it seems to have a problem finding and staying at a consistent vacuum pressure/throttle blade position and pulses back and forth just slightly with vacuum pressure varying from 11 to 9, back and forth.
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      11-18-2011, 09:36 AM   #13
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Perhaps this thread may help.
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      11-18-2011, 09:53 AM   #14
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Enrita does this issue still occur if cruise control is set or does it just do this when you are manually controlling throttle?
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      11-18-2011, 10:01 AM   #15
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Quote:
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Enrita does this issue still occur if cruise control is set or does it just do this when you are manually controlling throttle?
happens with cruise control as well.
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      11-18-2011, 10:06 AM   #16
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Quote:
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wow thanks, exactly same issue apparently . so canister might fix this? will change both and see.
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      03-06-2012, 06:12 PM   #17
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FIXED! changed almost all vacuum lines beside one and canisters, Cars runs like a champ now.
No more shaking, stumbling, surging at steady throttle etc. Seems gas consumption is lower as well.
Perfect throttle response. Basically another car.
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      03-06-2012, 06:45 PM   #18
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My SA said this had to do with putting BP fuel in my car and the high alcohol content of their gasoline (ie. my car's alcohol content was 15% when it shouldn't be above 10%). I'm not sure what this cat's alcohol content was when he told me this, but I have since changed gas and flushed my fuel system with Techtronic or whatever they recommend.

Vaccum canister sounds possible ... hopefully not expensive since I just came out of BMW warranty.
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      03-06-2012, 07:23 PM   #19
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Quote:
Originally Posted by enrita View Post
FIXED! changed almost all vacuum lines beside one and canisters, Cars runs like a champ now.
No more shaking, stumbling, surging at steady throttle etc. Seems gas consumption is lower as well.
Perfect throttle response. Basically another car.
good to hear. did you buy the vacuum lines from bmw? or just auto parts store?
how long of a line do you need to replace all?
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      03-06-2012, 07:31 PM   #20
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I bought all parts OEM BMW
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11657565963 Unterdruckleitung

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13717558227 Unterdruckleitung

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you can probably get them all from Tischer
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Parts : 1-5-6-7
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      03-06-2012, 08:44 PM   #21
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Thanks, will change that out.
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      03-06-2012, 08:49 PM   #22
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My car just started doing something very similar recently. I have just over 75k miles. Maybe I'll have to give this a shot if the shop doesn't get it sorted out tomorrow.
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