Topic: Z4 rough idle

[mmret]

Noticed something odd. In Park or Neutral, the car will have a vibration every so often (car "bumps" briefly, as if you have a gigantic subwoofer) and the RPM goes down a touch. Inconsistent but happens every 5-10 seconds or so. Doesn't seem to happen in drive.

Not throwing a CEL light though. Cylinder misfiring?

Now if I could only get my girlfriend to take it in...instead she is like "its probably just normal" and "I don't want to waste my time" (she is currently unemployed...all she has is time ). Women's brains must be made of mush because they don't churn out much in the way of logic. /rant

[vdk]

Women's brains must be made of mush because they don't churn out much in the way of logic.

Quoted for the unfortunate truth.

[huota]

I'm guessing it could be an engine vacuum leak, inoperative EGR or faulty ignition coils.

I had similar symptoms with my M54B30 engine and it was the coils.

Tell your girlfriend that if it's the ignition coils she will probably end up stranded on the road sooner or later, that should motivate her to take the car in.

[rrocket]

I suspect if there's no mechanical issue, it's the compressor from the AC cycling.  Inline 6s are silky smooth...and it seems I notice the "bump" of the compressor because there simply are no other vibrations.

[inco]

Is there an electric cooling fan on the car. Might be that kicking in and out, or the compressor as rrocket mentions.

[mmret]

I suspect if there's no mechanical issue, it's the compressor from the AC cycling.  Inline 6s are silky smooth...and it seems I notice the "bump" of the compressor because there simply are no other vibrations.

AC wasn't running at the time.

[mmret]

Is there an electric cooling fan on the car. Might be that kicking in and out, or the compressor as rrocket mentions.

That shouldn't cause an RPM drop though should it?

[Seafoam]

I suspect if there's no mechanical issue, it's the compressor from the AC cycling.  Inline 6s are silky smooth...and it seems I notice the "bump" of the compressor because there simply are no other vibrations.

AC wasn't running at the time.

It could still be running anyway depending if it's in the defrost setting or not.

[Careener]

It seems strange it would be as frequent as described if it's the AC. Sounds like it might be a timing issue.

[Turbo Bob]

Very odd, as that is a super smooth engine!

[dr_spock]

Bad gas?

[mmret]

Shell 91 =\

[blur911]

That's the sound it makes when it's crying because someone put an automatic transmission in it.

Could also be a sticky idle air controller, if it has one of those.

[Careener]

is there a rattling sound as well?

[mmret]

Nope, no rattling noises.

Its going in to BMW today but I have doubts as to my gf's ability to communicate the issue to a service department that'll probably try to charge her for warranty work (she is paying them for labour on something unrelated at the same time, .... in any case I sense this situation is ripe for abuse).

[inco]

Abuse - never.   It's called "pried from ownership" 

[rrocket]

Update?

[mmret]

Seems to have gone away on its own...the guy at BMW said given there's no CEL, if they diagnose and there's "nothing wrong" then they'll charge the customary $50 or whatever. Bleh. Will continue to monitor in any case...

Given that I am more likely to notice these things....good excuse for me to drive the car more.

[No H2O]

Does that car have an ''Idle Control Valve''?

Older BMWs had one that needed to be cleaned out every now and then.

Do a Google search.

[mmret]

http://www.partsgeek.com/catalog/2007/bmw/z4/fuel_injection/idle_control_valve.html

It appears that this part does exist. I'll look into it, thx hcrv.