weird thing happens when idle

[JohnyChevyEG]

My 01 LX makes a weird noise, and the RPM guage fluctuates a little when idle. This is usually after driving for a bit and then coming to a complete stop. WHen the lights are on, I can see the lights flicker when this happens as well. The noise sounds like a hum. It comes and goes. It will fluctuate rapidly for a few seconds and then start up again. Any thoughts?

[JohnyChevyEG]

I guess i should say that when the rpm guage drops, I feel a slight vibration as well. Thanks.

[ModMech]

Sounds like the A/C compressor cycling. When this is happening, turn the HVAC to the "OFF" position, and if it is the compresor, it will stop then.

[JohnyChevyEG]

Would it still do that even though I dont have the A/C turned on?

[ModMech]

Yes, in Defrost and "mix?" the A/C system is energised, and will run based on temp.

As I recall, the ONLY two positions on a Ford that kill the A/C system are "OFF" and "Vent"

[JohnyChevyEG]

I have it on the off position and it still does this.

[JohnyChevyEG]

I think I have narrowed it down to thimes that it occurs. I drive the car for a little bit then stopped in my driveway with out lights or anything else on, and it wasn't noticable. As soon as I turned on the headlights, it started doing it. I turned them off, and it returned back to normal. I also turned on the A/C and on the initial click as it was turning on, the rpm guage dropped real quick and I heard the vibrations then it came back up. COuld this be some sort of electrical problem? I have an appointment next tuesday to get this looked at, but I this thing doesn't happen all the time so I would like to troubleshoot it this weekend and try to fix it while it's happening. I would appreciate any suggestions.

[ModMech]

The "hum" might just be either the Idle Air valve resonating (which would explain the variable idle), a Power steering resonance (but that should NOT happen unless you are turning the wheel), or a belt tensioner/idler which is due to changing load on the belt system (alternator load, A/C compressor, P/S pump, etc).

[JohnyChevyEG]

How could I check these things. Sorry, I'm an extreme beginner when it comes to car work. I would like to become more interested in doing my own repairs though. Thanks.

[ModMech]

Well, if you step on the throttle, and the noise goes away, that points to the IAC solenoid. If it does not, then you remove the drivebelt and briefly restart the engine, if it's silent then you shut the engine off, remove the key and spin all the wheels that run against the belt to see if any are rough or make noise. Replace any that are noisy or rough (which should be done even if itdoes not completely solve your problem).

[JohnyChevyEG]

would the IAC still be the issue with the lights dimming when the rpm's are dropping as well?

[ModMech]

Sure, if the RPM drops becaues the IAC cannot maintain it properly the Alt output will also drop, lights will dim etc.

[JohnyChevyEG]

i seriously think thats it then. When I press on the gas even just a little, my problem goes away. Now, how can I fix this issue? Where is this thing located?

[JohnyChevyEG]

Nevermind, I found it. SHould I just attempt to swap it out? Or can I just clean it?

[ModMech]

You can clean it, but you have only about a 25% chance that it will be worthwhile. For $40, just replace it, and PLEASE use a Motorcraft replacement, the aftermarket stuff is truely not as good and costs just as much.