im having almost the same exact problem. when i start the car the idle goes all the way to 2100 rpm and very slowly drops to about 1200-1300 rpm. when im driving it and put it in neutral the idle will raise to about 2000 rpm until i come to a stop it will settle to about 1200 rpm. and when i come to a stop sitting at a stop light the idle will jump from 1200 to 1500 and then back down and back up a couple times. the car seems to idle way higher when it is colder outside at night. i also having a bucking problem from 1500-2000 rpms but after 2000 the car kicks in. what could be my problem?

 

I found that my tps 5v ref source is reading and fluctuating from 1.2 to 4.2 v. Not know what else to do, I will be replacing the pcm.