I have been fighting this truck for about a month now trying to find this, I'm guessing electrical issue. The truck is a 95, 4.3 w motor, 4x4 with OBD II. A few months ago I pulled the whole upper and lower intake and had all the carbon burned out of it til it was spotless. Not long after, went to start it, it about stalled, caught itself and brought the rpm's up to two grand and wouldn't come back down, does this often, not every time. Half the time I have to drive it two footed because it likes to stall when I come to a stop, half the time I come to a stop and the idle won't come down from 11-1200. If it sits idling long enough the idle will return to normal but as soon as I put it into park it shoots back up to about 1700. Only code it will give me is a P0122. Low signal voltage to the throttle position sensor. I back probbed every wire in the connector and all the way back to the computer and everything is exactly what it should be, although I replaced anyway, no change. Starting to wonder if IAC is having an issue but not totally failing. I can not find any vacuum leaks or any carbon build up. Pindle on the IAC was cleaned and it is not catching on anything in the intake. I don't know what else to check. Points coming from the IAC are coming back correct based on RPM on a scan tool. Any help would be greatly appreciated.

 

Finally another crappy '95. I just fought this same problem for nearly a year. Next time it is idling high, try wiggling the TPS harness connector and see if the idle instantly drops. Either that or you can wiggle the connector and the idle will jump high. I had a bad connection between the harness and the sensor. Voltage tests and ohming from the PCM revealed good connections just as you described. If wiggling the connector(plastic part) makes the idle speed jump, just save yourself the time and buy a replacement pigtail.

 

That's another thing, I've wiggled and pulled, no change.

 

when its ideling fine two things. Spray carb cleaner around all rubber hoses and see if you have vacume leak. Next like I posted in the higher then normal thread did you get the carbon build up off the idel control inside the throttle body. .02

 

I also had a big vacuum leak in the transfer case switch vacuum hose. There is a spot by the brake booster with a bunch of connections. Not sure if that's factory but it was horrible. If you don't want to spray carb cleaner everywhere you could just pull lines off the intake and cap them to see which one makes the problem stop. I've never seen an IAC stick open but have had them stay closed on a few different vehicles.

 

Does your temperature gauge work? Maybe it didn't get plugged back in when you put everything back together. With no temperature sensor input, computer won't know to set a cold or warm idle and will hunt or surge