What could cause high idling? 2000 rpm in park and 1500 in drive

Vacuum leak is a common cause, maybe excessive carbon build-up in throttle body. Possible faulty coolant temp sensor. Possible faulty idle air control motor....ALL CAN BE TESTED AND VERIFIED before spending money on incorrect parts! Try "alldatadiy.com" for technical specs and procedures. Small $$, may save big$$