When it happens in P/N and you place it in gear does the issues go away?
I am thinking check the fuel pressure at the rail. Maybe there is some variance going on and the tiny load while in gear puts enough demand to override. Similar to the AC being on

 

Okay, so I pressure tested it today. At idle while fluctuating or not I have a solid 50psi. From other posts I gather that 50psi is normal. I am wondering about the throttle body. It seems to be making some noises. Something like a sizzling sound sometimes that is very faint and also a very high pitched whine. Random clicks as well coming from the motor unit on the side of the throttle body. Are there any parts under that motor cover that can be replaced or is it a deal where you just swap the whole unit? Thanks for the reply Peter. How's TAB running?

 

Yep, 50 is a good number for the pressure.
Noises from the throttle body? And no codes?
Try cleaning it (throttle valve and electrical connections) and resetting it. Turn the key to KP2 (no start) and wait for 30 seconds. You should hear a "click". I always like to do it twice to be sure (KP2, click, key out, KP2, click, start).
If it is the throttle body then yes, it is replaced as a unit. But before you do: When the fluctuations are happening is the DME signal changing or just the actual RPMs? Engine data stream time. Lol
TAB is doing well :thumbup: although needs a bath...

 

Vacuum leaks take time to set codes. If you have live data you can check the fuel trims. Typically they must be above 10% for 255 times before a code will be stored. If you disconnect the MAF does fluctuating idle go away?

 

Vacuum leaks take time to set codes.

normally less then a tank of fuel

 

Okay a little more digging tonight. Hooked up to Creator 110 and ran some live data. While idling smoothly it says DME is sending 550 RPM idle signal. When the fluctuation starts it begins to vary similar to the actual idle. Scrolling a little further down my live data it says "Increase idle due to low positive battery voltage- ACTIVE. Is that normal? A quick check of the battery with my voltmeter says the battery is at 12.49V. The voltage reading from the live data (which I assume measures the voltage from the alternator) at idle varies from 12.9V to 14.1V. Can I assume that this surging voltage is due to the fluctuating idle or is it the reverse of that? Could a bad voltage regulator be causing my idle problem by forcing the DME to compensate for the low voltage thereby increasing idle until it reaches 14V? If that were the case wouldn't the ACTIVE switch to NOT ACTIVE once it hit 14V? Should my alternator be putting out more than 14V? I notice that the lights in the cabin and on the dash dim and brighten with the fluctuation. Also checked the MAF plug. When I unplug the MAF the car dies. Is that normal? I was expecting a change in idle maybe but not for the car to die. No sputter no nothing.......just shuts off straight away. After all the questions the one thing that still bothers me is the fact that when I try to bring the idle up with the gas pedal it creates a more intense fluctuation. It is very hard if not next to impossible to keep a steady RPM anywhere in the 1000-2000 range. Above 2000 and it can be held steady with the gas pedal. Lots to take in, I know. ANY input is greatly appreciated.

 

12.49 is not a good number at all *when a car is running..

Id start with a technical tap of the alternator it self, then move to connectors... The maf you just unplugged just made a new code.. clear that out and start over.
Put a volt meter on the battery terminals.. when idle'n you can even put the car under load if you want (electrical load)

It sounds like a voltage regulation problem.. some of these guys go thru the pain of tiring to repair instead of replace.. your call

 

The voltage fluctuation is likely the result of the unsteady engine speed. Sounds like you disconnected MAF with engine running. Disconnect before you start. Car should start and run. We want to know if idle quality changes.

 

Interesting: chicken and egg question but with rpm and voltage.
I can see the possible here so agree that more testing is needed but personally I think it will be the alternator.

 

Burning2nd's right about 12.49 not being good and the replacement.

Now that you mention it, I have the higher DME from low current too. I am sitting about 13.5 though (down from 13.7 in May when I ran my reference table). Technically I should r place the alternator/voltage regulator but it is still working, no light, and no code. So I am riding it a bit longer but I know it is failing. Playing chicken with the alternator.

 

The voltage you measured should almost be the battery voltage when car is off, with the car running you should measure above 14 volts on the terminals.
Like Burning2nd said, try tapping the alternator with a wooden stick or something.
All kinds of problems arise if battery/supply is not up to speed.

 

One thing I forgot to mention..... That 12.49V was the battery with engine off. Also, if my a/c is switched on the car idles smooth as glass. It never fluctuates. At idle with the a/c on the voltage measured on my reader is a steady 14.0V. I will test the battery with the car running and see what I get for voltage using my voltmeter. Thanks for the input.

 

If you are varying to 12.9 with it running then it is still "bad". You will have the idle increase due to low voltage. AC also increases the idle and may increase it out of the "fluctuation range".
It could be due to MAF or vacuum issues but I believe it is due to VR or alt on the way out.
Vehicle off: unplug MAF, start it and see if it fluctuates. If yes then likely alt issues. If no then could be MAF/vacuum.
It MAF/vacuum then clear codes, vehicle off, plug MAF in, start, watch lives data for MAF & O2 signals. I would expect that with that large of a swing a code would be set.
Did you reset the throttle body as I previously noted?

 

One other thing with the throttle body: check the pedal pentiometers to see what they are doing. Could be one or more is failing sending weird signals. Again, would expect a code but...

 

id think a throttle body pot problem would give EML/DSC lites, as well as codes. the system is touchy to a delta tween a and b channels. this thread is very interesting as to what and why. just talking outa the side of my mouth, but low rpm low voltage could be the regulator in the alternator, or other alternator problems, as his battery readings seem to be good. might just give a shot to reading battery voltage after idling for 5 mins with hi beams on. ac fan on hi, then shutting it off and seeing what it reads. warming up there yet TAB? we hit a lil over 80 today.

 

whats the voltage @ the battery terminal under full load idle'n?

*lights, seats, wiper, blower, defroster, *hell if you want to go ocd, cig lighter pushed in lol

bear's has got this in post 14

 

Not a whole bunch of time today. Checked the voltage at battery but forgot to run full load on it. Idling it was reading 14.2V. I'm in the middle of some body work on my dads car. Hoping to button that up tomorrow and get back to the idle problem.

 

There is a good chance this is not related to your issue, but for Diag purpose, I need that number under load,

Next we will move on to live date, and or downstream secondary input

 

Okay under full load.......13.3-13.4V. Even had the rear defrost on. LOL

 

This is more than adequate and not the cause of the unsteady idle.
Did you ever start/run w/ MAF disconnected?

 

Thats no good....

you need @ least 14.1-2

your gonna have to sort that out....
YOU are sure sure sure positive thats your charge? try giving the alty a smack with 2x4 see if you can bump that volt up a volt and a half, Id hate to send you on a goose chase, but Its hard to diag any further with suspect charge voltage

target is 14.2 to 14.7

 

So I checked the MAF again for those that asked. Same result connected or not so that is ruled out. However I think I may have stumbled onto my answer........kind of:dunno:. Sitting with the car idle loaming up and down I was pissed at all the flies buzzing around me. So I rolled the window up. When I did this the idle flattened out. So I rolled all the windows down and waited for the idle to start moving again. when it seemed at it's worst point, I rolled the windows (all of them at once) up and wouldn't you know the idle smoothed out again. I performed this experiment a few more times with the exact same results. Seems that with a load on the alt. the idle smooths out. What exactly does this mean? Not sure, as I'm no expert. But I am hoping this clue may help someone else out in pointing me in a direction. My gut says either the regulator or alt. is nearing the end of the road. What say you? Easier to replace the regulator or should I just replace the whole damn thing.....It does have 190,000 mile on it.

 

Do that experiment but with test 9 and see what the current is doing.
Maybe it is a connection to the alt? Not enough juice and there is voltage drop?
More likely the VR or alt.
I would go for the shebang, 190k is respectable.

 

No change w/ MAF disconnected rules out vacuum leaks, bad MAF and issues related to closed loop operation. Interesting observation about the windows. I don't think this indicates an alternator problem though. Operating windows puts a load on the alternator which in turn puts increased load on the engine. This increased load is similar to having car in drive and you don't notice the speed fluctuations in drive either. I'm thinking your high mileage throttle body can't control at small throttle openings needed for no-load idle.

 

Interesting... so to diagnose this would be to watch for TB open values vs rpm?

 

Yes. Not sure if you can see throttle position with INPA/Rheingold. It would be interesting to see if throttle position is changing while idles speed is fluctuating or is it fully closed and leaking due to wear/age. Are there driveability issues with car in gear? If not, i think I'd ignore this problem.

 

Accelerator meters seem to check out. There is no fluctuation in voltage when i slightly depress the pedal it steadily climbs even as the the idle swings. Same can be said for voltage at throttle body. However even when bringing the car up to 1100 rpm the throttle opening still shows 0%. If it rises above that it will show 4% open. No issues when driving it's just irritating as hell because it makes the car sound like a beater (which I guess it really is ). I will get to the bottom of it sooner or later.....or maybe I will move on. I would really love a 540i/6.

 

......... when bringing the car up to 1100 rpm the throttle opening still shows 0%. If it rises above that it will show 4% open........

How are you reading this data?
This car doesn't have an idle control valve, correct?
This is very interesting......the throttle plate is moving, but the DME doesn't know the position has changed at least for the first 4% of travel. Is this normal or does it indicate a problem with position potentiometers? Need to run similar test on another 540i for comparison.

 

Creator c110.....live data. It's buried in the back pages of data. Like 23 or 24.

 

I will try and use my 310 for a reading tonight after the kids are down to make sure but...
Looking at my reference values (http://www.bimmerfest.com/forums/showthread.php?t=910726) at idle I was 2.4%. 1100 was 3.1% (roughly).
Might have a winner.