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Do you know where the wires go to?
I dont think it is the SPOUT as it does not look to pull apart.
I want to say it holds a Diode - a 1 way valve for electricity.
The IAC is controlled by the ECM grounding the IAC solenoid in a "duty cycle" The valve in the IAC "floats" toward open and closed many times per second. Each time the cycle ground opens, the diode allows the voltage spike to be reabsorbed into the power circuit.
Edit. The newer IACs have the diode built in. So, I think '85-86 are the only years that have externally mounted diodes. The newer ones have a small triangle embossed on the solenoid. Fun Fact: the triangle is actually a "Delta", or D for diode.
Last edited by diggerrigger; Jan 3, 2026 at 08:00 AM.
Hay I gave a hint on what it was just did not know what for
I want to say I seen one on the harness for the 81 F100 but did not trace it out at the time.
Dave ----
I think when the IAC is bad, the truck can stall at times when you put it in Park.
Mine does, sometimes. I recall about 15+ years ago, the trusted mechanic said something about it... I think. I have not worried about it. I've learned to watch the idle when going to Park and just catch it and give it a little gas to help it idle. So for me, it's not an issue.
Thanks for the info. Never seen them before. Do they go bad and if so, what is the effect.
The spikes from the IAC would eventually ruin the computer. You can check it easily enough. If you put your ohmmeter on it, it should read low ohms one way, high ohms the other. It's just a electrical check valve. You do have to install it correctly or will mess things up.
To test the diode, disconnect battery and unplug the IAC. You can now check the diode by probing the IAC connecter. You will get continuity one way and no continuity the other. Current flow direction is embossed on the diode. I recommend back probing the connector to avoid the possibility of damage.
EDIT: To make back probing easy pull the silicone seal out of your way.
Last edited by diggerrigger; Jan 4, 2026 at 10:36 AM.
