philup

ok so i just noticed a few days ago that my car has this weird idle problem but its not like most people talk about on here.. ok so the other day i pulled in to my drive way and my car was warm from about 10 miles of driving and i noticed my idle was about 1500 and it would bounce from 1500 to 2000 but so i rolled my car back a little and pulled it up and i noticed it dropped down to 900 and stayed there ? so i rolled it back again and reved it up to around 3 grand and rode the cluch a little and i saw that if i push the cluch in at more than 3000 my car will idle at 1500 bouncing to 2000 but if i push it in running at like 1000 i have a normal 900rpm idle i dont really understand why and i would like to know if anyone has seen this before and how they fixed it.. please and thank you