Idling Troubles....Please Help

[RPeters]

I have a 1987 420 SEL that is idling high. I put some octane boost in a half of tank of gas. It ran fine for one day, but is now idling between 1300 to 1500 rpm and is starting to surge. What should I do. Any suggestions is greatly needed and appreciated.

[JEFFMG1]

Many post on high idle. Do a search.

To get you started here is a list of things to check on in order of likely cause.

ovp relay
idle control valve(ICV) bad or need cleaning
idle control unit
Major vacuum leak