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      12-01-2008, 03:15 PM   #1
Mr. 5
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Rough Idle and Fluctuation During Deceleration!

It's bugging me and I was curious if anyone had any issues with what I've described.
I know about the fuel pump horror stories but it seems that this would be something different.

I have no problems starting the car.
My RPMs go from 500-600-500-600 at idle.
During decleration while in gear, the car seems like it doesn't know what to do.

Any info on this?
Bad gas maybe?
Please don't say it's the fuel pump.
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      12-01-2008, 03:20 PM   #2
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Quote:
Originally Posted by Mr. 5 View Post
It's bugging me and I was curious if anyone had any issues with what I've described.
I know about the fuel pump horror stories but it seems that this would be something different.

I have no problems starting the car.
My RPMs go from 500-600-500-600 at idle.
During decleration while in gear, the car seems like it doesn't know what to do.

Any info on this?
Bad gas maybe?
Please don't say it's the fuel pump.
When you say deccel, do you mean foot completely off the throttle (ie, engine braking)? 6AT or 6MT? And what do you mean by fluctuation?

shiv
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      12-01-2008, 03:20 PM   #3
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Quote:
Originally Posted by Mr. 5 View Post
It's bugging me and I was curious if anyone had any issues with what I've described.
I know about the fuel pump horror stories but it seems that this would be something different.

I have no problems starting the car.
My RPMs go from 500-600-500-600 at idle.
During decleration while in gear, the car seems like it doesn't know what to do.

Any info on this?
Bad gas maybe?
Please don't say it's the fuel pump.
I had the same exact issue, as well as a bunch of others; even when stock. The "rattle fix" that was just recently implemented in v3.1 completely eliminated the rough idle. I'm guessing it has something to do with the wastegates...
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      12-01-2008, 03:31 PM   #4
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Quote:
Originally Posted by Mr. 5 View Post
It's bugging me and I was curious if anyone had any issues with what I've described.
I know about the fuel pump horror stories but it seems that this would be something different.

I have no problems starting the car.
My RPMs go from 500-600-500-600 at idle.
During decleration while in gear, the car seems like it doesn't know what to do.

Any info on this?
Bad gas maybe?
Please don't say it's the fuel pump.
This sounds like what I got...rough idle/misfire type behavior at idle and just cruizing..and when decelerating. When I am accelerating..car works fine. I took off my Dinan tune...so the dealership can figure this out..and NOT blame the tune. It is getting worse..my car has been at the dealership numerous times for this...here is what I have gotten replaced so far:

1) FOUR HPFP..yes, I said four!
2) Fuel Pump sensor
3) Two coilpacks (dont know which ones..just said two of them)
4) ONE fuel injector (dont know why they didnt do all of them)
5) Waste gate rods? (something to do with waste gates)
6) Throw out bearing (nothing to do with this issue)
7) Starter (nothing to do with this issue)
8) TWO Brake pad sensors (nothing to do with this issue)
9) TWO sets of Rear Brake Pads (nothing to do with this issue)

P.S. I am now on Progman 31.1 (I think)

I dunno guys..but none of my Audis ever had all this stuff done in 20 months/29K miles of ownership.

This is getting really old.
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      12-01-2008, 03:56 PM   #5
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This may be stupid but is your gas cap on correctly?
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      12-01-2008, 03:57 PM   #6
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Quote:
Originally Posted by shiv@vishnu View Post
When you say deccel, do you mean foot completely off the throttle (ie, engine braking)? 6AT or 6MT? And what do you mean by fluctuation?

shiv
For example, approaching a traffic light:
Downshift to second, foot is completely off the throttle, engine is declerating, but the engine decelerates-decelerates not as fast-decelerates-decelerates not as fast-decelerates-decelerates not as fast-etc.
This happens smoother than what is posted but hopefully you get the point.

Quote:
Originally Posted by S4to335 View Post
This sounds like what I got...rough idle/misfire type behavior at idle and just cruizing..and when decelerating. When I am accelerating..car works fine. I took off my Dinan tune...so the dealership can figure this out..and NOT blame the tune. It is getting worse..my car has been at the dealership numerous times for this...here is what I have gotten replaced so far:

1) FOUR HPFP..yes, I said four!
2) Fuel Pump sensor
3) Two coilpacks (dont know which ones..just said two of them)
4) ONE fuel injector (dont know why they didnt do all of them)
5) Waste gate rods? (something to do with waste gates)
6) Throw out bearing (nothing to do with this issue)
7) Starter (nothing to do with this issue)
8) TWO Brake pad sensors (nothing to do with this issue)
9) TWO sets of Rear Brake Pads (nothing to do with this issue)

P.S. I am now on Progman 31.1 (I think)

I dunno guys..but none of my Audis ever had all this stuff done in 20 months/29K miles of ownership.

This is getting really old.
This sucks man and I feel for you!
It's weird because it just happened out of nowhere.

I was wondering if my lightweight battery was the culprit because I had to charge it the other day since I ran it down while messing with my sat radio.
I checked the coltage while driving to work this morning and it was fine.
It fluctuated between 13.5V and 14.9V
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      12-01-2008, 04:48 PM   #7
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Mr.5, this may be totally unrelated but your last post made me think of it - the 335i (and other modern BMWs I suspect) use regenerative charging of the electrical system I believe under decel condtions - I'm uncertain if the lightweight battery would cause the strange decel you're feeling, but I wonder if perhaps they are related? Maybe this regen system requires the stock battery (or like capacity) for the system to be "happy" and not see any sort of resistance...

Just throwing it out there, may be wildly off base of course.

Snipped from an Edmunds article - more to be found out there I'm certain :


Active electrical management


Just as turbos recoup energy that would otherwise be wasted as heat, the energy dissipated while slowing down can be put to good use. Gee, brewing up a nice hefeweizen would be — no? OK, how about producing electricity, then? It takes horsepower to make electrical power. Thanks to the alphabet soup of electrically powered doodads in modern cars, the alternator sucks down an ever increasing amount of horsepower.

Called "Brake Energy Regeneration," BMW's solution is to plop in an oversized battery and engage the alternator only during deceleration. By actively controlling the alternator and battery charge electronically, the alternator just freewheels happily during cruise and acceleration while the battery supplies the necessary juice for the car.

Referring to this system as regenerative braking is something of a misnomer. True regenerative braking implies that the batteries are the prime motive power source, when in fact BMW is still using the battery in a conventional manner to power auxiliaries. The system is rather clever nonetheless. And in the EU drive cycle, Brake Energy Regeneration alone reduced fuel consumption by 3 percent and freed up to the drive wheels the power that otherwise would have been used to turn the alternator. It's a kind of free lunch. Just without the beer.



Theory : under braking, this recharging during decel is topping up the lightweight battery more quickly and disengaging the alternator. Battery use resumes, system sees the drop, reengages the alternator. Assumed here that it's smaller, like a Braille? - I have a Braille in my Elise and it's good for just about 3 starts at the track when fully charged - great battery, in small bursts! But it charges very fast, and I wonder perhaps if this is taking place in your car and throwing this fancy FM system off a bit.
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      12-01-2008, 05:28 PM   #8
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Quote:
Originally Posted by Bubbles View Post
This maybe stupid but is your gas cap on correctly?
I think you found the problem man.
My cap was on but I took it off and put it back on again.
I started the car and there was no fluctuation.

When I drive home, this will be the true test.
I really hope that you got it.
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      12-01-2008, 06:04 PM   #9
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Quote:
Originally Posted by Mr. 5 View Post
I think you found the problem man.
My cap was on but I took it off and put it back on again.
I started the car and there was no fluctuation.

When I drive home, this will be the true test.
I really hope that you got it.
hmmmm... Thats weird. I thought it would throw a CEL if your gas cap was not all the way on. I hope that fixes your problem
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      12-01-2008, 06:08 PM   #10
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hmmmm... Thats weird. I thought it would throw a CEL if your gas cap was not all the way on. I hope that fixes your problem
Yeah..that is what I would have thought.
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      12-01-2008, 06:55 PM   #11
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Quote:
Originally Posted by Mr. 5 View Post
I think you found the problem man.
My cap was on but I took it off and put it back on again.
I started the car and there was no fluctuation.

When I drive home, this will be the true test.
I really hope that you got it.
Good luck, let us know how it turns out.
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      12-01-2008, 10:27 PM   #12
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I drove home and that wasn't it.
It is pretty weird.
No codes or lights.

It's kind of like the engine is straving for air for a split second and then not and then starving and then not, etc.
It's also only enough for me to tell.
I drove my friend to lunch and he couldn't tell.
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      12-01-2008, 10:35 PM   #13
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When in deceleration, the car is no longer in closed loop fueling mode, it goes to open loop... not sure if it helps to know that when trying to find the culprit... I was just trying to think of things that change during decelleration...

Do you still have the jb3 installed? I would try pulling it out just to make sure its not a loose wire issue.
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      12-02-2008, 12:27 AM   #14
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Originally Posted by RiXst3r View Post
When in deceleration, the car is no longer in closed loop fueling mode, it goes to open loop... not sure if it helps to know that when trying to find the culprit... I was just trying to think of things that change during decelleration...

Do you still have the jb3 installed? I would try pulling it out just to make sure its not a loose wire issue.
Yah but it's strange that it just happened out of nowhere.
I've had it installed the entire time.
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      12-02-2008, 07:08 AM   #15
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Quote:
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Yah but it's strange that it just happened out of nowhere.
I've had it installed the entire time.

Sounds like an invite to the fuel pump party.
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      12-02-2008, 09:12 AM   #16
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Do you have access to a Wideband monitor, say a LM-1 from Innovate?

I would like to see if the A/F ratio changes greatly? It shoudl shoot to about 20:1 during the decel period and stay there. I wonder what specifically the fuel is doing.

I forgot to look, MT or AT? If AT, the DME should shut off fuel completely for a moment. If MT and out of gear, the DME has to maintain the idle.

One test I would try imediately is changing out the battery back to stock. I wasn't aware of the loading of the engine through the alternator and battery and that could have an impact. Plus, you should not be seeing voltage levels up to 14.9 VDC, that is too high.
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      12-02-2008, 10:48 AM   #17
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I believe I have fixed the problem.
I believe it was due to a clogged PCV.

A while back, I took out my catch can to mess with the rear actuator, so I attached the 2 hoses to bypass the CC.
These hoses are kind of long and they made a loop verticaly.
I've been driving like this for over a month.

I'm thinking that the oil/gases didn't have enough pressure to vent and therefore was clogging the PCV.

This is also one of the reasons why I was having no problems under acceleration and not deceleration.


Scalbert,
I don't have a wideband monitor.
I don't know exactly what the upper bound was with the Voltage but if it were 14.1 would that be too high?
It was definitely in the 14s and I will bet if you did the same test as myself then you find almost exactly the same readings.

It's menu 9 in the secret menu.
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      12-02-2008, 10:55 AM   #18
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Quote:
Originally Posted by Mr. 5 View Post
I don't know exactly what the upper bound was with the Voltage but if it were 14.1 would that be too high?
It was definitely in the 14s and I will bet if you did the same test as myself then you find almost exactly the same readings.

It's menu 9 in the secret menu.
14.1 would be fine. 14.9 is a high swing though. 13.5 - 14.5 is typical while driving.
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      12-02-2008, 11:02 AM   #19
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14.1 would be fine. 14.9 is a high swing though. 13.5 - 14.5 is typical while driving.
OK, I'll look at it again to make sure.
There's a definitely swing though when I go from something like 3k rpm down to idle.
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      12-02-2008, 11:02 AM   #20
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OK, I'll look at it again to make sure.
There's a definitely swing though when I go from something like 3k rpm down to idle.
It should drop at idle as the alternator is turning slower.
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      12-02-2008, 06:46 PM   #21
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OK guys, it was definitely the PCV.
It's all fixed now.
No idle fluctuation and no weird decleration.
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      12-02-2008, 06:49 PM   #22
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Glad to hear it was a relatively easy fix! Thanks for sharing the results.
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