My 97 540i is having some issues. It idles pretty low (~350-400) and it has a hissing sound from the intake area. Hissing sound is somewhat consistent at most rpms. It almost like it's misfiring, but I am hearing a hissing sound from the intake area.

I checked the vacuum hoses and tried spraying brake fluid around the intake, but nothing. Car has no CEL on, everything else is fine with the car. Anyone
has any ideas how to troubleshoot this?