warmup sequence idle - is this normal, read desc.

hey guys everytime i start my car instead of idling at ~2000rpm like its supposed during the warmup sequence it jumps up and down every second for about 7-8 times, from 2000, drops to 1000, then revs back up on its own, i thought this could be a vacum leak, but i cant seem to find one, let me know if you guys know anything about this, also, my car seems to rev slower now…