Ford Repair: engine running ruough on idle, bronco ii, vacuum leak

Question

I have a 86 Bronco II with a 2.9  What it does is when idiling it will drop up and down in RPMS by about 700 RPMS.  But if you run the headlights it runs smoothly.  What could be up with that?

Answer
I have not heard of a problem like this, and haven't seen a Bronco II in a long time.  Most of the time, a rolling idle is caused be a vacuum leak.  I can't think of any reason for the headlights affecting the idle, other than increasing the load on the alternator and engine.

I hope this helps,
Dave