AchtungE60

It could be many different issues. MAF is one of them...not too familiar with the V8 so not sure if it has the double vanos but you could also have sludge buildup from infrequent oil changes or not using recommend oil...or the DISA etc etc...get youself some BMW diag tools and to monitor the situation. I had misfires in cylinders at idle and the car would choke. I found the problem and it was the intake manifold air flap. Fixed in a few minutes and car has been fine...no need to spend $200 on a part when you can fix.

DavidF

Ok, here is another possibility...don't laugh, it was true in my situation. My '04 545i behaved almost exactly as described when I purchased it used. I narrowed the cyclic groaning noise to the alternator and using my INPA software, I monitored the voltage of the alternator and noticed it would fluctuate between normal and low in unison with the groaning notice. So, my thought was that the alternator was cycling between load and no load and the engine DME was struggling to maintain a steady idle as a result of the cyclic loading unloading of the alternator.

So, I removed the alternator and took it to the rebuild shop. Diagnosis: failed rectifier, if memory serves (a non replaceable or rebuildable part). So, I had to replace, not repair, alternator. Problem was solved and idle remained steady afterwards.

Just saying.

syrousd

Those damn rectifiers!!!!!

dave_ctt

Interesting update...

Dropped someone off at the dealer today so I decided to bring this issue up with the shop foreman.

This is what he said:

My battery was replaced and registered about a Month ago and he said this is normal behavior. The computer lost all of its settings and needs to re-learn everything including normal idle cycles and it will get better over time as the car is driven more. I'm not sure I'm buying this but the one thing that is driving me nuts is I started noticing it around the time the battery was replaced. Now I'm wondering if it was like this before the battery was replaced and I just didn't notice it until recently. (I've only had the car about 5-6 months) In any case, I'm cleaning the MAF this weekend for sure to see if anything changes.

dave_ctt

Interesting update...

Dropped someone off at the dealer today so I decided to bring this issue up with the shop foreman.

This is what he said:

My battery was replaced and registered about a Month ago and he said this is normal behavior. The computer lost all of its settings and needs to re-learn everything including normal idle cycles and it will get better over time as the car is driven more. I'm not sure I'm buying this but the one thing that is driving me nuts is I started noticing it around the time the battery was replaced. Now I'm wondering if it was like this before the battery was replaced and I just didn't notice it until recently. (I've only had the car about 5-6 months) In any case, I'm cleaning the MAF this weekend for sure to see if anything changes.

pcy

Voltage Regulator is usually attached on the back of the alternator. Voltage regulator can be replaced [for around $100] without having to replace the entire alternator. If you chose to replace the alternator because of the age, that's a different story.

In the picture below, part #5 is the voltage regulator.

DavidF

You failed to read my post carefully. It was NOT a matter of a failed voltage regulator, but instead a failed rectifier which is not replaceable.

DavidF

Explanation sounds like complete hogwash to me. I propose that the faulty alternator caused the battery failure and thus the problem persisted. Upon replacement of my alternate, the idle quality instantly improved and the cyclic droning stopped. Remove the alternator and have it tested

dave_ctt

I agree. I was thinking the same thing after hearing his response. Just thought I'd share it. They blamed my battery failure on "Unfavorable Driving Profile".

bluelightning3

To anyone who has surging RPM's and crazy error messages. Just replace your alternator with a voltage regulator(which comes with a reman) and everything will be good as new!!!