i dorve to a store and everything was fine. then i came out and started the car. its rpm shot to 2500 then stayed there. turned the car off and let it sit for a few seconds. started back up and check engine light came on. car ran fine driving home but when sat idling in drive way was fine. raise to 2000 rpms and the car slowly went to idle speed and then almost wanted to stall out. what could be wrong with it?? i checked all the gauges and they looked fine.