I've got a 97 Ram 1500. Everytime after driving I put it in park and it starts idling high and then I can put it in drive and it'll drop back down to normal. On occasion it'll idle high for a minute when I start it. I can hear the whistle on the driver's side but I don't know what vacuum lines to look for.

 

There aren't that many...... Spray around the area with carb cleaner, or something similar. See what you are spraying at when the idle changes. Likely that is your problem.

 

I think they like to break where the go through the firewall on the passenger side. Would affect defrost and cruise control IIRC.