intermittent slightly rough idle ?

[fairchild]

The next part I have on order is a code reader. I am just now seeing how the engine runs (now that I have a tag and insurance)
So far it is running reasonably well-- except when it is well warmed up it some times gets a bit of a "rough" idle. It will last maybe 5 min.
and then go away for a while and then come back. By the feel I cant quite tell if its a coil pack dropping out to if the timing is shifting
(as in a bad cam sensor) or if the vanos is needing attention. I have not seen any weirdness in the 1000 to 2000 RPM range as I have read that
vanos can do (at least so far) I have no way of knowing if the vanos had been fixed by any previous owner.
I suppose it could be a intake bellows leak ? If I shoot wd-40 over it and see if the engine sucks it up and revs up a bit--- will that tell me ?
Or---- do I just need to wait till I get the scanner ? (am I just wasting my time before the scanner is in hand.....)

Is the only way to figure out the vanos --- to take it apart and change the O-rings ? Or test for codes for a few weeks and see what shows up ?

Thanks-
Tim

[328 Power 04]

Well what code scanner are you getting? The BMW factory tools will log vanos angles and you can see response time to judge if it's operating well.

But I think you likely have a vacuum leak or a dirty idle control valve.

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Is check engine light on?

[Blacklane]

The usual symptom for bad VANOS seals is lack of low-RPM Torque. That's not what you describe.
Look for a vacuum leak, particularly the boot downstream of the MAF. It could also be a bad CCV causing a leak. It could be a bad MAF, but those aren't typically intermittent.
A scanner can help if you know what values are right. Note that a code reader is different from a scanner. A code reader just reads stored failure codes. There has to be an out-of-tolerance condition to set a code and you might not have that. A scanner reads the values of various sensors and reports those. It takes a great deal of expertise to know the proper values for all of the different conditions.