92 ranger engine runaway

[lineman1997]

First time posting here, been reading for years. Driving my 1992 Ford ranger (4.0 v6) and out of no where the motor started screaming, turned the truck off while coasting and turned the key again to hear the engine running away. I pulled off on the shoulder of the road and the throttle cable was fine. I wiggled the cable and cranked the truck back up with no luck. Sat there for 20 minutes, wiggled the cable some more and she cranked right up and drover her home no problem. Thanks guys

 

[Dirtman]

Check your throttle position sensor.

 

[.38spl]

Along with the throttle position sensor, also check the throttle body. Pull the tube loose from the TB, and check the butterfly and the bore for carbon buildup. I have also seen the small screw come loose from the butterfly/ shaft and get hung between the butterfly and the bore.

 

[Oxxon]

Hello and welcome to TRS!!

 

[The Donald]

Also check your idle speed motor and wiring, it may go haywire and start doing what it wants, letting air into the engine regardless of what the computer is telling it to do.
Edit: Maybe remove it and check the valve seat and valve and make sure nothing is obstructing it closing tightly. Any air thru there possibly makes the idle go up.

 

[RonD]

Welcome to TRS

AIR..................you can only get higher RPMs on a gasoline engine(or diesel) by adding more air
If you add more fuel engine will just flood and stall

So air is your issue
I would first pull off the "air tube" that runs from air cleaner to upper intake, then have a look at the throttle plate that closes off the intake, this is the main air flow restrictor for gasoline engines, and it should have a strong spring that "snaps" it closed when you test its movement, if the spring breaks then throttle plate can't close off air flow when engine is running

On fuel injected engines an air valve is used to set idle, Ford calls theirs the IAC(idle air control) Valve
It is capable of RPMs as high as 2,500 if it sticks open

Good read here on cleaning IAC Valve: https://www.explorerforum.com/forums/index.php?threads/iac-valve-cleaning-thread-w-pics.84220/

You can test IAC Valve by removing it, and then hook up its 2 wire connector
Turn key on
Look inside at the valve and unplug the 2 wires, valve should move and close, only moves 3/8" but moves
Plug wires back in and it should move to fully Opened
Repeat as much as needed to determine if its working or not

You must use a Motorcraft IAC Valve if you want to replace it, there have been many reported issues with 3rd party IAC Valves
A used motorcraft IAC Valve from wrecking yard is better than new 3rd party IMO