1990 Toyota Pickup high engine idle

I have a 1990 toyota pickup 4x4 6cyl engine. When I start the truck up it idles around 2K RPM. Sometimes I can hit the gas and and the idle will drop back down to around 1K RPM. Its almost as if the throttle body gets stuck. When it does go back to 1k RPM the gas cuts off and rpms drop to 500RPM and then the gas kicks back on and jumps up to 1200 RPM. Most of the time though its around 2K rpm. Does anyone have a clue what the problem is?

I think if I adjust the idle then thats just going to mask the problem and not solve it.

thanks to anyone who reads this and suggests a solution.