Erratic RPMs. Any ideas?

[juggernautjan]

Hi, We have a 1997 4.0 and all of a sudden the revs started to show between 1500 and 2000 when we shifted into neutral from drive. Then crept up higher to 2500 but came slowly back down to about 1000. Then whilst driving, revved itself up to 2500, and would not come down, so we switched off the engine, then restarted and she was revving at 6000!!!! After a little cooling off period, restarted again and she seemed to be more or less okay for a mile and a half whilst we drove home. Does anybody have any ideas what that could be please?!
Thanks, Jan

 

[Sams01XplrSprt]

welcome juggernat

 

[BrooklynBay]

Welcome to this forum! I've moved your thread to the stock 95-01 section. Check for a vacuum leak.