My car is the Base RSX 2003, 5spd. I noticed this today, and was wondering if this is normal or not. I was idling after a 10-20 minute drive, parking brake on and transmission in neutral, and rpm was around 650. When I blipped the throttle, it would rev up to 1500-2000rpm, and then dip down below 650 for about 1-2 seconds, and then goes back to normal idle. Blipping again while the revs are low causes knocking/pinging or chain rattle kind of noise momentarily right as the revs start going up. What are some causes of this? Anyone have experience fixing this issue? Thank you in advance!