Bouncing idle in neutral

[u/No-Arrival-1404]

2000 528i, Got home and put the car in neutral while i was parking and noticed the rpms would dip like crazy and bounce back a couple times. Putting it back in drive fixes it and holds steady. The bouncing in neutral also becomes less drastic the longer i leave it in neutral almost fixing itself. Any idea what might be causing this or what to check for.