1994? Grand Marque, sudden very high idle.

Daughter called for help. Increased idle started suddenly, not dropping engine speed at stop light. If left without brake, will reach about 20 mph. Stayed same when started after parked overnight.
No help spraying linkage. When I see it later this week, will check linkage for frayed cable. Is there anything else which commonly causes high idle? Clogged PCV valve? Bad vacuum line? Bad electronic component? Rat nest under air cleaner? She states no symptom above 30 mph, and accelerator peddle does not stay down or appear binding. I just want to be able to test all causes, and save her a buck.
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wrote:

It is not likely a linkage problem although it is a good idea to eyeball it anyway. You likely have either a vacuum leak which usually occurs int the PCV circuit on those or a dirty/bad IAC. The IAC can be cleaned but, they are many times too carboned up to easily clean. Overnite soaking of the valve end in a good throttle body or carb cleaner may work. Sometimes, they require replacement. They are usually available for around $50 or less if you can replace it yourself. It is not difficult if you have a decent assortment of hand tools. Sometimes, it is best to remove the whole throttle body and clean the EGR ports at the same time which is often needed on that vintage to correct or prevent other problems. You will need a throttle body gasket to do that.
Good luck Lugnut
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Besides PCV, check the entire Vac accessory system
Could also be bad IAC motor
4ax.com:

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