I just bought a 1991 Bronco Silver Anniversary with the 5.8 engine. When first started it idles fine but if I drive it at all and then put it in Park or Neutral the RPMs jump to 1500. Occasionally it won’t give me this problem. It seems to idle fine in gear when stopped. I’ve checked the IAC and it’s fine. I don’t expect a vacuum leak or a worn throttle body because it’s not constant. I’m not sure where to go from here. Any help is appreciated. Thank you.