When I start the car, the engine idle is fine. Around 1400 and drops when it warms up. The problem occurs when I go for a drive and come back home. When I put the tranny in neutral or park, the idle goes up to 2000 RPM and it stays there. If I turn the car off and turn it back on, it goes back to normal idle...until I put it into neutral then back to park. The tranny also jolts hard as soon as you put it into gear because its at the high rpm. What could be causing this? I hear IAC or loosen cable on TB.

Its my dad's oldskool 89 Integra RS...trying to sell it. Any help appreciated! Thanks