Having pretty much the same problem, same code# p1506, havent replaced anything yet but on a budget and looking for answers also.
I have a 97 ranger that will idle like its at full throttle. It doesnt do it all of the time, but it has been doing it alot lately. If you push the clutch in and put it in nuetral while driving the rpm will rev WAY UP like its at full throttle. Lubed the cable and mech on top of throttle body, cleaned the IAC valve with carb cleaner. The pedal, cable and mech operates smoothly. wondering if there was an EASY WAY to test the IAC valve ?Any suggestions would be great. I dont have much money to work with and it is my only vehicle as of right now. I have read other people replacing alot of things and still having the problem and I cant really afford to buy a bunch of new parts that dont do anything.

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1997 Ranger 2WD (210,832 miles and counting.....)
4 cylinder (2.3L)
5 speed manual

RIDE IT TILL IT DIES !