Ford 4L V6 fast idle

Hi Folks, I'm wondering if anyone can direct me to a troubleshooting list for looking into a fast idle (2000+ rpm) problem on an old 1992 Explorer that is
in otherwise top notch working order. Thanks, BCinBC
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For free info that's pretty accurate, autozone.com is good.
Can I ask a couple questions? Do you have a Check Engine Light illuminated? Can you hear a vacuum leak anywhere? Does it happen all the time?
There was an oddity about my 1992 Ranger 4.0 that not many people would know about. Every once in a while if it didn't start right up, the compression would make the engine kick back a little. Two times when it did this it blew a vacuum plug off the vacuum tree on the intake. It was very strange, and if I were like most people, I'd have never known what was going on. I actually heard it pop off both times with my then-young ears, and both times I found the vacuum plug lying under the truck.
Just a thot.
CJB
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The story on this V6 is that I just bought it from my neighbour & I know he spend a fair bit on money on trying to get the idle down. I think a mechanic replaced the AIC valve last week but the day I bought it the idle was still quick & since there was a blizzard at the time I didn't open the hood. But today the sun was out so I checked it over: No there is no service engine light ( it's not burned out -checked that). I don't hear any vacuum hiss & took a quick look at the vac hoses + wiring -looks OK at first glance. Turned over for a few seconds before starting, then would stall at first going into D unless a bit of gas applied. After a few minutes then not a problem for P to D. However after maybe 15 minutes the idle speed does pick up in N or P at just under 2000. I am not about to put this on the road for a month or so but I would like ideas as to what to check for, so thanks for your response. BCinBC

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