shaky idle?

hi hope you can help me.i own a bmw e36 318is coupe,automatic,1998.1.9l..it has a shaky idle when cold an when warm.the ccv or breather valve and hose been replaced.new sparks oil filters.new o2 sensor.been smoke tested twice with no sign of leaks.the revs stay constent at 600/700rpm with no fluctuating.the car seems to drive smooth/fine. ive noticed theres a constant hissing noise coming from manifold to??? plz help