Start with the basics
I would first check the basics: your spark plugs/wires, rotor, air filter, fuel filter, clean your MAF, and check your IAC. Also check and make sure you do not have any vacumn leaks. I could be wrong, but from what you have said it sounds a lot like your IAC, or even a vacumn leak.
Are there any check engine lights or codes thrown?
I am sure there are also other people here who have other ideas as well. Just my 2 cents! Good luck!