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Ok once in a while when I turn on my 2002 Ford F-150 the RPM's go from 1000 to 800 then back to 1000 over and over and this is at idle. I haven't gone to get it looked at and I want to see if it's something I can fix at home. Anyone have any suggestions on what it can be?

  • Clean your IAC and see if that doesn't help. – Pᴀᴜʟsᴛᴇʀ2 Nov 21 '15 at 1:57
  • Also clean your throttle body as well. Be sure to get the back side of the throttle plates and any holes in the plates. – vini_i Nov 21 '15 at 2:16
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I will keep my answers fairly simple, as the procedure will differ, and I'm unfamiliar with your vehicle.

Clean the MAF sensor. It is a very thin metal filament inside a circular component attached to the throttle body. It's purpose is to measure the volume of the incoming air.

Clean the throttle body. All the incoming air passes through the TB. While the air filter removes a large portion of material, some may get through and collect on the throttle body inlet which is a very small-holed screen.

Replace the idle air-control valve(IAC). The IAC controls the amount of air passed through to the engine base on information from the MAF and what is allowed through the TB. They're all intertwined.

Coincidentally, I will be doing all three personally, as my will car will not start until I give it gas. The battery powers the components, and the starter is initialized, but I have to get it some acceleration, so if anyone has a similar issue, try the methods mentioned above.

*some one let me know if I'm correct, I'm just answering to help cement what I know (or don't).

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    Agree. I think the idle control valve will be OK, since the engine ECU will be controlling the idle control valve and making the revs go up and down. Definitely clean the internals of the throttle body. The MAF Sensor is very delicate, so clean it with an appropriate spray. – HandyHowie Nov 21 '15 at 9:59
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    @HandyHowie - How do you consider the IAC will be "OK"? If by "OK" you mean "it's working", then I'd agree. Problem is, it's not working correctly. The first place to look at is the IAC when the engine is searching for an idle position, since it is what controls the idle (via the ECU). Cleaning it should be the first task on the list for getting things right. – Pᴀᴜʟsᴛᴇʀ2 Nov 21 '15 at 14:06
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    @Paulster2 I would suggest that the butterfly is probably closed completely due to gunk and the ECM is trying to correct by opening & closing the IAC, causing the surging. I wouldn't replace the IAC as suggested in this answer until the other options have been checked. I agree with you that cleaning the IAC may help too. – HandyHowie Nov 21 '15 at 14:28
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    Or possibly the butterfly is not closing enough and the ECM is having to go to the full limit of the IAC to drop the revs, then it trys to bring it back off the full limit and the revs go back up. – HandyHowie Nov 21 '15 at 15:03
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    @HandyHowie - Either way, a complete and thorough cleaning of the intake tract will probably cure the issue. Clean before replace makes the car happy and the pocket book happier :-) – Pᴀᴜʟsᴛᴇʀ2 Nov 21 '15 at 15:22
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A vacuum leak after the MAF sensor could also cause this. I would do this before replacing any parts, since it doesn't cost anything (if you have some starter fluid lying around).

This YouTube video might be of use.

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