I think TwinTurboGTR is referring to the Secondary Air System. See attachment. Stuck open Non-return valves could allow exhaust gas to get sent to your secondary air pump, but I wouldn't expect this to cause rough idle problems.

I would spend the $35 and review all the SIBs for Group 11 (Engine) and Group 12 (Engine Electrical) on bmwtechinfo.com

Great info, but how does one test/clean/inspect them?

You could disconnect the air pump after starting a cold engine and feel for the blower to output air and simultaneously there should be no exhaust gas coming from the opposite end.

This graphic is from the E65 training literature (also from bmwtechinfo.com), but it should be similar for the E53 X5 with the N62B44 engine.

Ok, this is good stuff. I am guessing since my engine is 4.8, but still N62 this would also apply.

Seems like there is a lot of tubing there that could be leaking. I am going to check this out tonight.

So let me get this straight.
So if I disconnect the hoses at number 5 or at both number 4s, I should get air coming from the blower, but then I should also not get exhaust from same hoses/valves telling me if the check valves are functioning.

I think I got it. I just hope I can get to that pump easy enough without removing the entire intake.

Will this throw a check engine code? If yes, I need to go get my scanner back from my friend before doing this.

On a second note, can I test those check valves off the car. I have an air compressor I can use to blow through it. I am just curious how much that valve can handle. I am guessing it is not much PSI going through there.

Thank ripp.

Ok ripp. so this was a fail. I should have checked RealOem before standing over my engine for over an hour. I don't seem to have this. My engine is 4.8. Any other advise? Thanks.

I didn't know you had a 4.8is and hence a N62B48 engine. You are correct, no secondary air system.

Assuming you have rough idle, I'd still read all the SIB's to see if there may be one pertaining to your car. Then I'd have all the fault codes pulled.

OK. I figure you don't have it, so I guess I might have to do this TIS thing.

I have a 2006 4.4 with the same symptoms. Idle around 525 with vibrations. I have only owned the car for a month so I don't have much to compare to (was it always this way?) but it just seems rougher than it should be (rougher than my 5.7 sequoia) and with a little extra rpm it smooths right out. If anyone found solutions. Please send an update.

Idle fluctuation
 

Changed wiring and MAF, improved but still had a leak.
When removing the oil cap with car running you should hear the air entering otherwise you have a leak. After spraying the intake with carb cleaner no change, meaning no leak in this part. Finally, the shaft seal gave up and sprayed oil on the belt, that grew bigger and came out. After replacing the Shaft seal problem solved! Hope this helps.

Sounds like a vacuum leak problem to me.

Sorry if this has already been suggested, I didn't read the entire thread.