I rev my engine when its on park (I have the AOD) and the RPM hangs at 1.2K then drops to 1K and then it very slowly drops down to like 700rpm or 500rpm depending on how long i ran the car. Sometimes when i rev it, it drops down a little and goes back up and down then finally drops back to the normal idle rpm. When im driving and im accelerating then letting it idle, the engine will keep at the rpm i left it after and only when after a while it will go back down to normal. I have cleaned the IAC and the MAF. is it a dirty throttle body because when i took out the plastic tube leading to the throttle body, the butterfly door looked pretty clean. What should i be looking for when i check the throttle body? Could it be the tps going bad?