Put the S13 back on the road today

well i put my car back on the road today stayed up till 4am putting the new rad in so i cold get it on the road today… anyway the car is running great except for one thing i notice the idel is high. when the car is in gear sitting it is aroudn 750 but when it goes into park it goes up to like 1500 i am wondering if the throttle cable just needs time to get moving again or is it somethign else…
thanks
Brent