DodgeForum.com - '04 Stratus sedan engine probs

Hi all, new to the forum so please bear with me. I have a '04 stratus se sedan. Got it w/ 21,000 miles on it and currently have 51,000 miles. I love this car but it is killing me with an engine problem. It has the 2.4 4cyl. in it and I have been having a rough idle/driving/stalling problem. When the car is at idle the engine seems to "surge" for lack of a better word. The rpm's will shhot up tp maybe 1500 then right back down to around 500. I can't run the A/C beacuse it causes a stall in the engine. I noticed this problem at maybe 30,000 miles and changed the plugs/filters etc. and it went away. It has come back recently and is getting steadily worse. My check engine light has come on and I ran the diagnostic test on it. The code was P507 "Engine rpm not as expected" or something like that. The engine light just came on yesterday and now when you accelerate the car hesitates and gets sort of "jerky", like it isn't shifting. I am unable to find any sort of trouble code list to help me out and I really don't want to get raped by the dealer by bringing it in. Any suggestions or anyone else notice a similar problem?