3 different times very recently went to start car & eng. just spun over & on 5th time it started, also when slowing down to approx. 15-20 mph the rpms would jump up to about 1300 rpms & not drop back down for minute or 2, if I lightly tapped gas pedal it would go up then drop back down to about 700 rpms then go right back up to 1300 rpms & eventually settle back where it's supposed to be. And today (09/21/2019) was heading into town & only went approx. 3 miles coming to stoplight, while coming to almost a complete stop the rpms jumped up again & when the light changed I went to take off & it died & wouldn't start until the 5th try, decided to go back home, it ran a little rough most of the way home. My question is: could this be a computer problem? Also I recently installed a reconditioned motor 1900 miles ago, the previous engine was overheated badly from previous owner, Could this possibly have affected the computer (ECU)?