Weird idle problem

[s13coupe88]

Hey so first off I tried to google this and I felt like most of the post i saw wasn't similar to my situation.

Car info240sx s13 KA24E freshly swappedNew royal purple oil and K&N filterNew air filterI put in some fuel injector cleaner into the gas tank AutoNo air conditioning beltThe car does have a hole on the exuast, but its a fart cannon so im going to replace it anyways.

My car is idling funny, when the car is in park or neutral it idles at 950-1100 rpms at the start but after a few seconds/minutes it goes up to 1500. When its in drive/reverse it idles at 750-850 rpms. I bought the car a couple of weeks ago and the engine was freshly swapped a couple of month ago. I knew the car was idling a high but i had a good deal and I just wanted to be in a 240 instead of a kia lol.

I honestly didn't understand a lot of what i read online but I tried lowering the idle from the ECU by turning the screw, but it didn't really do much.

What do you think the problem may be?

On a side note, i just changed the oil from some cheap oil to royal purple and the car idles 150 rpms higher is that normal?