Hi All,

This may be a well known issue in 2006 BMW 523i N52 engine , or similar models.

ISSUE: Idle Fluctuate between 640 - 680, More often on engine operating temperature. while stoping at stoplight car shake little bit, rmp drop to ~630 for couple of sec and then raise up to normal. And then idle fluctuation continues.

DIAGONOS AND OBSERVATIONS:
1. Vacuum leak test - No Vacuum leak identified. Replaced new oil separator and hose, new Intake manifold gaskets, new throttle body gasket.
2. Vanos test - Tested the Vanos in INPA, nothing strange. Swapped Intake and Exhaust vanos solenoid. still nothing changed.
3. MAF sensor test - MAF reading 2.8 - 3.2 g/s at idle which fluctuate up and down waveform the MAF reading graph up and down match with the idle rpm up and down. SHOULD MAF READING BE STADY AT IDLE? , or IT CAN FLUCTUATE BETWEEN 2.8 - 3.2 AT IDLE?

4. **** Battery Charging system Test :
- Now while testing the Battery charging system something which I am not certain about. I hope You guys can clarify me.
- While engine at idle the battery voltage is between 14.7 15.0v .
- In INPA the the DME Voltage Supply and Battery Voltage Fluctuate between 14.40 to 14.90 and this fluctuation match with the idle engine rpm up and down between 640 - 670 . Please check the video attached.
- ***But the most strange thing which I noticed. At idle there is sudden dip in the DME voltage supply value from 14.60 to 12.60 for couple of second and again raise up. Along with it the idle rpm also dip to around 600 rpm for couple of second and raise up. Please check the video attached. IS THIS VOLTAGE FLUCTUATION from 14.60 - 12.60v with IDLE DIP AND RAISE NORMAL?
- Checked the alternator belt - fine. Alternator positive terminal- Good and clean. But.. There is a single pin harness connector connected at the back of the alternator, Guess it is to the voltage regulator. While ignition ON, i checked the input voltage on this connecter, it was only ~6.80 - 7.10 . WHAT IS THE CORRECT VOLTAGE ON SINGLE WIRE PIN ALTERNATOR REGULATOR HARNESS CONNECTOR ?





I Hope some one could help me. I love this car, but this idle fluctuation making me mad for last 1 month.

Thank you.

 

Hi,
I hope you’ve already solved your problem but if you haven’t, maybe this will help. I had an identical symptom to what you described. My Indy shop checked many of the same things an no joy. Finally discovered it was a broken DISA valve, on the intake manifold. A piece of the flap had broken off and it wasn’t maintaining consistent air flow. Replaced and car ran perfectly. Good luck, I hope this helps.

 

wow, i exhibit similar symptoms, except i'm also getting a buzzing noise as well... i'll take a look. 06 530xi.

it's getting worse and i'm feeling resistance. i'll check the disa since i am hearing this weird plasticky rattle.

however, the idle fluctuations and roaring i'm hearing from the engine bay sound a lot like a bad alternator pulley as well...

 

Funny thing, when my mechanic took the DISA out, he couldn’t account for one small missing piece. Shortly after I got it back there was a clattering sound in the engine for a bit, and it went away. We figured it was that little missing piece bouncing around and it eventually made its way out through the exhaust valve.

 

I have an 04 525i that's doing sort of the Same thing only during accelerating from a stop or very low speed problem kicks in around 28-35mph & rpms bounce between 15-20k unless I let foot off gas for a sec then issues gone when applying gas again. I used injector cleaner & it somewhat helped, I think its something in injector or maybe something caused by a power fault somewhere cuz for some rand on reason the fuse has poped multiple times as well as a charger I have with display says my powers always fluctuating lower than it should be, I had battery checked b they said its fine so maybe some other electronic issue.