Hey I'm new to the forum I have a 94 Ranger 4.0 OHV it started idling at 500rpm after I did the heads, I think I know what it is by reading other threads here I need a second opinion before I go start throwing parts at the problem. I'm thinking its the IAC when I unplug the IAC no change a cures for a couple of seconds then the truck dies. Any recommendations to problem would be greatly appreciated. thanks in advance

 

Welcome to the forum

Take the IAC Valve off the engine and then plug in its wires
Turn key on, IAC valve should now be open all the way
Now, while watch the valve inside, unplug the wires, and it should close, then plug them back in and it should open, repeat as you see fit

It only moves 3/8" or so, but WILL move if its working

Motorcraft or Hitachi brands are the only ones that will work as replacements

 

is that key on engine off or running?

 

Key on, engine off

The computer, on boot up, opens the IAC Valve all the way for start up, sends it full 12volts
The it lowers the volts when RPMs are above 400 to set target idle

So key on sends 12volt and IAC Valve opens all the way, unplug the wires, 0 volts it closes all the way, repeat as you see fit
The IAC Valves metal case does not need to be grounded, the two wires are all it needs for 12v and Ground

You can also test the 2 wires with volt meter to make sure wiring is OK, assuming valve is not moving, should see 12v with key on

 

ok thats how I checked it and it didnt move about to go get one Ill update when installed