What cause the engine to have a "fast/high" idle.

My engine runs great, but idles around 800 constantly(hot or cold, may vary by 50RPM or so, going off top of my head)

What controls the high idle as i thought it should idle around 1100-1250 when it is cold then drop down to 750-900 once warmed a little.

Its a 86 Ford Ranger with a 4D55 incase anyone is wondering....