Greetings from Finland! Have you tried that when you are at park and idle goes to 1500, can you lower it by turning steering wheel to extreme right and left positions? I did a lot of testing with WJ DiagPro injector learn values to make fuel corrections numbers as small as possible. When fuel correction was big in some cylinders, I had this same issue that idle did not lower down after measuring 1500rpm. Moving steering wheel from left to right did lower it.
And when I got those fuel correction values to good numbers, idle setled fast to 750rpm after measuring with 1500rpm. I remember reading from somewhere that injector giving too much fuel causes high idle.
In image are my numbers. Left is starting point and right is what they are now.