bigtinybob

when i first start the car up it idles fine an when i put it in drive it does good,but after running it for awhile an i put it in park an then pull it back to drive,the rpms die down to like 4 or 500 an if i tap the gas it will jump to like 1000,but if i pull it back in drive an dont touch the gas it wont jump to around 1000,could this be a idle sensor or something