A couple things come to mind. a vacuum leak, the iac (idle air control motor) is stuck, make sure the trans cable/linkage isn't froze. or since you have a shifting problem also, My money would be on the tps (throttle position sensor) If the tps is within it's spec it won't set a code. a scan tool to read the sensor would tell you right away. you could also read it with a digital volt /ohm meter, need a schematic to tell you what wires to read from. It works on a 5v reference. The sensor at idle should read a touch less than 1.0v and wide open is in the 4.5-5 v range. sometimes a temporary fix is disconnect the battery for a minute or so and let things relearn. a scan tool to read the sensors would pinpoint the problem in minutes.