04 dodge ram idle problems?

[Albert s]

Hello i have a 4.7L dodge ram. and yesterday after driving it a bit i came home put the truck in park and the rpms were almost at 3000 rpms. i hit the gas and it went back down to 600. why did this happen? I have a new throttle posistion sensor and i cleaned my throttle body. and the other day i tried starting it and it took longer than usual and when it started my Engine light came on. I have not got it checked out yet. but today the engine light didnt come on. What could it be? can it be the IAC sensor? can this be cleaned? thanks