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Discussion Starter · #1 ·
Well lads and ladies, I'm getting the feeling, more and more, that
there is something wrong with the VANOS in my '03 325i.
As some may be aware, I've had an "odd" idle issue with my 325i from the day I picked it up and drove off with this beauty. In fact, I noticed an odd idle with my 325i before I even drove it for the first time. So, from the time I got my 325i with 5 miles on the odo I've had an odd erratic idle which fluctuates from about 600rpm to 900rpm. It does this less often and with less erratic
behavior on warm days and does it more often in cold winter weather when the temps drop below the mid 30's F. And, when it's really cold out, below freezing, and I turn up the heat in the car my idle will actually RISE to about 800-900rpm and that will become the "new" idle. It then fluctuates once it reaches it's "new" higher idle. My MPG drops to around 17-18mpg and that's with a 5 speed manual shifted around 3000rpm with mild acceleration, mixed city/highway.
BMW is aware of this. They have documented it after quite a few dealer visits and at least an hour of "discussing" the issue with a BMW Certified field technician, who kept claiming that "its' normal". After failing to demonstrate this normalcy of erratic idle behavior in another 325i, even his very own, he finally said, "hmmm...seems there is something going on." :)
You think!?

So, that "discovery" by said field representative was "filed" with BMW NA who were to "work" on the problem and come up with a "fix". I love using "" as it makes it all seem so "sure, we'll fix it."
That was finally acknowledged around March of 2004. I complained of the problem in May of 2003 with 5 miles on the odometer. When cold weather finally set in in the Chicago area, around November, I took the 325i in again to have the dealer techs take a look with no success.

Now, all this time I've had the experience of something very strange during hard acceleration. By "hard acceleration" I mean pedal to the floor WFO throttle and shifting at just a hair before readline. The strange part is that I would occaisionally feel this odd "pause" or "stumble" in the power just as I would shift. From 1st to 2nd at redline drops you in the power band somewhere around 4500rpm (check me on that I could be off).
So, I'm in 1st, redline, shift to 2nd, WFO throttle, accelerate, feel of slight power loss/stumble/pause then power comes back full on, redline, shift to 3rd, repeat...It's not that noticeable after the shift to 4th and 5th as most times the isn't enough room to keep accelerating to redline before the real world is coming at you very quickly.

I have almost 20k miles now and I've noticed this pause/stumble is more prominent than before and the pause/stumble is getting very annoying.
It makes the whole driving experience much less fun and makes more angry that it's there.
I now think these two things, the idle and pause/stumble are related.
Doing some reading into the workings of the VANOS setup it seems that it may be the culprit. VANOS works to keep idle smooth, which in may cases it doesn't. And, it works to allow shorter or greater cam timing duration over the rev band.
Now, VANOS is not V-tech thus it is "supposed" to work steplessly, meaning it is continuous and variable. V-Tech is a preset "switch over" to in the cam timing so it comes on at a predetermined engine speed.
However, it's appears that the continuos part of the VANOS does not necessarily mean that the driver won't feel it come on or off, at least not when it is working correctly. The VANOS is controlled (on/off) by oil pressure which is activated at around 5000rpm. That seems to coincide with where I'm feeling this strange pause/stumble in my power output.

Here is a link to some VANOS operation information.
http://www.armandduco.com/News/Achives/Vanos/WhatIsVanos.htm

Here is portion of some of that info:

"At idle, the cam timing is retarded. Just off idle, the DME energizes a solenoid which allows oil pressure to move that cup gear to advance the cam 12.5 degrees at midrange, and then at about 5000 rpm, it allows it to come back to the original position. The greater advance causes better cylinder fill at mid rpms for better torque. The noise some people hear is the result of tolerances that make the sprocket wiggle a bit as the cup gear is moved in or out."

It is around that particular rpm, 5000, that I'm feeling the power loss in my 325i during hard acceleration. The power delivery is NOT smooth but choppy right in that rpm range. And, along with my erratic idle problem I'm really starting to suspect that there is at least some relational issue with my VANOS unit.

If anyone has experienced the problems I'm describing and has some insight into how VANOS is or is not contributing to my problem PLEASE feel free to post.

TT
 

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SST said:
I've had the experience of something very strange during hard acceleration. So, I'm in 1st, redline, shift to 2nd, WFO throttle, accelerate, feel of slight power loss/stumble/pause then power comes back full on, redline, shift to 3rd, repeat...
i don't have the idle problems you mention, but do experience the heistation. but mine occurs randomally across the entire RPM range. have you expereinced your problem ONLY during redline shifts ?

btw: i haven't found a fix yet. dealer isn't helpful and neither is BMWNA. from the various forums i have a list of possible problems: VANOS unit, plugs, throttle body, clutch, accelation pedal adaptor, faulty fuel pump, software.
 

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and the fluctuating idle seems to be fixed by the 39.1 or 39.2 software recently released..

my idle is rock solid now..
 

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Iniquity said:
and the fluctuating idle seems to be fixed by the 39.1 or 39.2 software recently released..

my idle is rock solid now..

how do you upgrade the software?? do you take it in to bmw service??
 

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Discussion Starter · #6 ·
vaio76109 said:
The dip at roughly ~4200rpm is from the intake manifold switching over runner length. Its normal.
The dip is higher up not around 4200rpm. And, if that were "normal" I'm sure we would have read about this in the many reviews this car has received. Those who have experience with vehicles would have surely noticed such an annoyance in the power band. This isn't something that is that subtle in nature. This is a straight up BIG power dip, much more so than the typical dyno results show.
The 2.5 engine dynos do show the power "dip" that I'm feeling, but in my 325i is not so much a dip as a drop.

Thanks for trying with the intake, and I will bring it up with the BMW tech, but I'm still with the VANOS unit here. I'm looking at the two big issues in my engines operation which are both affected by the VANOS, namely the idle and the power drop around the same rpm where the solenoid activates the oil pressure.

So, by "normal" you're saying that under heavy acceleration you too feel a big dip in power around 5000rpm?
Is your idle steady and solid as well?

TT
 

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Discussion Starter · #7 ·
Iniquity said:
and the fluctuating idle seems to be fixed by the 39.1 or 39.2 software recently released..

my idle is rock solid now..
I've had a software upgrade which was done in early spring. I was then told that my car had the updated software anyway.
I have a 2003 325i.

Which vehicles, 325 or 33, are the 39.1 and 39.2 updates for? Orginally, the techs and BMW thought my car needed a software update until they realized that I actually had the latest software as of 3/04.
Are these updates of recent vintage? If so, when was their release date?

Thanks.

TT
 

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SST said:
So, by "normal" you're saying that under heavy acceleration you too feel a big dip in power around 5000rpm?
Is your idle steady and solid as well?

TT
Under heavy acceleration I feel it at around ~4200rpm. And people have commented on the power dip there before, its nothing new.

No, my idle fluctuates. Im gonna get the DME reflash when i go back to TX, and also have them look at/replace the cam sensor.
 

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Discussion Starter · #10 ·
vaio76109 said:
Under heavy acceleration I feel it at around ~4200rpm. And people have commented on the power dip there before, its nothing new.

No, my idle fluctuates. Im gonna get the DME reflash when i go back to TX, and also have them look at/replace the cam sensor.
Not to put too fine a point on it, but the power "dip" is not something truly noteworthy as just about every publication has NOT mentioned it.
In fact, the engine wins awards regarding it's smoothness all across the rev band from idle to redline. And, it gets accolades about how smooth the torque delivery is from a few rpm past idle to redline.
It's true. Every other BMW 3 series I test drove (about 6) was very smooth and had a nice steady idle.

I'm not discussing the typical running conditions of these engines. I'm trying to get at a condition that is atypical of these great engines.

It was pretty cold this past Saturday in the Chicago area and just like last winter my engines idle went up about 300rpm and then that became it's new idle. It happens when it's cold outside and I turn the temp control above 76F or around there. Once I do that the engine speeds up to around 900rpm and that becomes the new idle. You can hear the higher engine speed. Then, after a minute or 2 the idle starts to go up and down a bit and you can hear the engine speed going up and down.
Last winter my mileage sucked, literally :). I was getting 17-18mpg with slow driving, all shifts made around 3000rpm.

So, in light of all that, I can't accept that this is "normal" engine behavior, especially when other 3 series don't do this.

Thanks for the suggestions and help.

TT
 

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SST said:
Not to put too fine a point on it, but the power "dip" is not something truly noteworthy as just about every publication has NOT mentioned it.
In fact, the engine wins awards regarding it's smoothness all across the rev band from idle to redline. And, it gets accolades about how smooth the torque delivery is from a few rpm past idle to redline.
It's true. Every other BMW 3 series I test drove (about 6) was very smooth and had a nice steady idle.

I'm not discussing the typical running conditions of these engines. I'm trying to get at a condition that is atypical of these great engines.

It was pretty cold this past Saturday in the Chicago area and just like last winter my engines idle went up about 300rpm and then that became it's new idle. It happens when it's cold outside and I turn the temp control above 76F or around there. Once I do that the engine speeds up to around 900rpm and that becomes the new idle. You can hear the higher engine speed. Then, after a minute or 2 the idle starts to go up and down a bit and you can hear the engine speed going up and down.
Last winter my mileage sucked, literally :). I was getting 17-18mpg with slow driving, all shifts made around 3000rpm.

So, in light of all that, I can't accept that this is "normal" engine behavior, especially when other 3 series don't do this.

Thanks for the suggestions and help.

TT
Well during cold starts the idle raises to ~1000rpm for about 30 seconds and then drops back down, which is perfectly normal.

If you idle dips and raises that is also a known problem. Usually a DME reflash will fix it. Altho sometimes its cam sensors...
 

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Discussion Starter · #12 ·
vaio76109 said:
Well during cold starts the idle raises to ~1000rpm for about 30 seconds and then drops back down, which is perfectly normal.

If you idle dips and raises that is also a known problem. Usually a DME reflash will fix it. Altho sometimes its cam sensors...
Please reread my posts in this thread. This has all been covered and tried.

I'm quite familiar with the raised idle on cold start in just about every engine. :)

TT
 
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