99 Cherokee park or neutral rpms climbing to 2800! What is causing this idle sensor???? Thanks

 

Probably the Idle Air control Valve , to the left of the Throttle Position Sensor when viewed from in front. Take it out (torx bit T25 IIRC) , clean it with throttle body cleaner, not carb cleaner, and a toothbrush.
Do not move the pintle that slides in n out.
Reassemble and you may get lucky and not have to replace it.
Could be your TPS but I would clean/replace the IACV first. They're not too much.

 

Thanks will check that!!!

 

When you clean the tb do yourself a favor and get a new $2 gasket, thats where i had an issue in the past