2001 Chevy Lumina LuckyLumina

Hello! 2001 Chevy Lumina with 148000 miles. Never ever has given me a problem that I haven't inflicted on it myself. Now, when I slow down (like at a stop light) and when I'm driving slowly (through town) and when I put it in park. My engine seems to be speeding up, the RPM meter gets higher, and my car seems to be possessed by the devil. Its as if I'm pushing the break but someone else is pushing the excellerator and causing the engine to soar. Called a mechanic and he said something about a small motor but I can't remember what he called it. Said it causes the rpm's to stay going fast when the car slows down. Also, car has died twice in the past 2 weeks while going slow or when approaching a stop light. Any Idea what could be going wrong with my car?