So my 2005 545i has a idle issue. Mostly it's at 500 rpm idling and you can wheel the car shake but some other times it's at 750rpm which is pretty regular. Now I do have a check engine light for the secondary air pump. Could that cause the idling issue or are they not related? If not related what could cause my car to idle at 500Rpm

 

I'm usually at around 500rpm without AC and 750ish with AC. Check your CCV Valves as well as the secondary air pump.

 

Would surely fix that pump first if still an idling issue . Than do what I did when I got the car two yrs ago idled like sh#%^t, dealer SM told me to drive like I stole it as car had been driven by an old guy, I drive in sport mode when not on the freeway all the time, these cars need to be driven with higher Rpm's than what you get during normal NA driving.
Taken awhile but car now idles good.