Mitsubishi Montero Sport Idle Issues
 

I have a 2000 Mitsubishi Montero Sport Limited with the 3.5 L engine. It was idling kinda low and unsteady so I took a look and the throttle body was pretty dirty. I cleaned it out and now it idles stable but kinda high.
Before cleaning it out, it would idle between 750 and 900 rpm in Park. After cleaning it, it idles at 1500 rpm in Park.

It's become an issue because the truck jerks when I put it into reverse. In the mornings when it's cold, I put it in Drive and the rpm's go up as if it was in Neutral and then it jerks forward after a few seconds. After I drive it around for a while and the transmission fluid warms up it shifts fine the rest of the day. I'm afraid that I may cause damage to the transmission if I keep driving it like this.

I was wondering if disconnecting the battery would reset the idle or if I have to reset the ECU.

ps: I wanted to adjust the idle screw but it's missing so no luck there.