rpm drop

Hi all first just want to say I love how helpful this forum and community is, this is my first post but have come here for awhile to find answers whenever I've had a problem. However this time is several different problems at once and don't know what to do or where to start. 2007 Caliber R/T...

So today I was sitting in my car with the engine running and the car in park while my girlfriend ran into the store. All of a sudden the car would slightly shake and the RPMS would drop 150-200 RPMS and feel like its going to stall but doesnt and then quickly shoots back up to where it was. It...