IAC Testing Help

[hashcraft]

Hello, I have a 1993 ranger with the 3.0 engine. It starts right up, but has a low, rough idle, almost like a muscle car. This video matches what mine sounds like:

1.8K views · 6 comments | Any ideas what would cause this rough choppy idle? Idles fine when cold but after the truck warms up it does this. 1993 3.0 liter. TIA | Grady Piel

Any ideas what would cause this rough choppy idle? Idles fine when cold but after the truck warms up it does this. 1993 3.0 liter. TIA

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I've been doing a bunch of research and a lot of people said to start with the IAC valve. I read that if you take the IAC off but leave the wire plugged in, the plunger should move up and down when the key is flipped on. When I flip the key on, the plunger moves up maybe half a millimeter.

I bought a new SMP branded IAC and it doesn't move at all. You can feel a little 'jerk' when it gets power, but that's it. I read these run on 12 volts, so I made a plug and briefly touched both the new and the old IAC valve to the battery, still no significant plunger movement from either. Both have 10-11 ohms of resistance and I read that they're supposed to be between 7-15 ohms, so they're both in range.

I have a motorcraft IAC showing up in a couple of days; I also read they're the only ones worth buying. In the meantime, can someone verify if the IAC plunger in supposed to noticeably move when they key is flipped on but the engine isn't running?

 

[franklin2]

I have never verified that. I do know the computer controls it, so if the computer decides not to move it, it's not going to move. Does the computer move it open a set amount when you are getting ready to start? Not sure. But I do know the computer adjusts over time or "learns" for different valves and different conditions, so you might try disconnecting the battery for a minute to clear the learned information, possibly that would make it start fresh.

I have also found out messing with these things, that it really doesn't settle down and act right until you have run and stopped the truck over several days. This must be part of that learning process. It can be very frustrating.