Re: setting the idle on a 92 bronco
I once had a 92 bronco, only it had a 5.0L--same difference though.
I had the same problem. Though I later learned that there were several smaller problems causing it.
First, you can adjust the base idle, but you shouldn't. It's computer controlled and if it isn't idling right, something is wrong. But if you want, there is a set screw on the throttle body that adjusts the closed throttle position.
The first thing to check is the Idle Air Control valve (IAC). This is a small electric motor mounted on the throttle body which controlls idle speed electronically. If it quit, this would certainly cause the problem. You can test it by removing, running 12 volts to connections and seeing if it moves. Often these get dirty and stop working or simply wear out.
other problems that cause this would be related to ignition problems such as base timing and simple misfires. Ignition diagnoses are another forum though.