My 89 Vandura 5.7 lit. idle's so high that when I put it into gear it slams pretty hard into gear. Anyone know how to adjust the idle or whatever I need to do to fix the problem?

Vacuum leak. Unmetered air entering throttle body will cause high idle. There is no adjustment. Or I don't know if a 1989 has a TPS, Throttle Position sensor, it probably does. The butterfly in the throttle body may not be closing all the way. Listen for a sucking sound, or hoses off, or nipples with nothing attached, all will cause a vacuum leak

Thank you for reminding me

Yes , same thing happened here, it was the vaccine line going into the throttle body, wasn’t hooked up