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Weird rpms?

696 Views 7 Replies 3 Participants Last post by  TimTom64b
So I have this strange thing happening with my motor I will be sitting at a stop foot on the brake and my rpms will jump from a 500 idle to about 1200 just for a second then come back down. I don't get it has anyone else experienced this?
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What year and model is the truck? Motor size? Mods done (tune or chip)? Last tuneup? We need more info to help you
I would check the iac. It could be sticking or failing. Here is a procedure I found on another site to check the iac. I have seen a bad iac cause this problem. But I have also seen other issues like vacuum leaks cause the issue

You can check the health of the valve by checking its resistance. When you disconnect the IAC valve, connect an ohmmeter to pins 2 and 3 of the valve. If you get a resistance value between 10-14 ohms, it indicates a functional IAC valve. Now, connect the ohmmeter to pins 1 and 2. If you don't get a resistance value between 10-14 ohms, this means, the IAC valve needs a replacement.
1995 are tbi and don't have a maf. There is a MAP sensor that is mounted on the intake manifold
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