Idle RPM Drops When I Turn On The Headlights

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Feb 13, 2013 | 02:52 PM
  #1  
These issues started couple weeks ago. My car currently idle around 600-625. When I turn on the headlight the idle RPM drops to 600 or little under 600 and idle rough and then goes back. If I turn on the fog light the RPM drops lower and sometimes even to the point I feel the car is going to stall.
Also, since these issues started when I turn on the headlight I hear low level whining noise coming from the speakers and when I turn on the fog light the whining noise gets louder. Any idea what causing these issues? Thanks
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Feb 13, 2013 | 03:05 PM
  #2  
What's the condition of your battery and alternator?

Id suspect one of those is about to crap out shortly. Might want to swing by a parts store and have your electrical system checked out.
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Feb 13, 2013 | 10:27 PM
  #3  
Quote: What's the condition of your battery and alternator?

Id suspect one of those is about to crap out shortly. Might want to swing by a parts store and have your electrical system checked out.
Battery is a year old and alternator is original. When i turn the heated seats i don't have these issues, does the lights use more energy then the power seats?
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Feb 14, 2013 | 01:39 AM
  #4  
I notice a slight change in idle when I turn my headlights on as well. Nothing drastic enough to make my car idle rough though. I just figured it was because the HIDs were kicking in.

Maybe I'll pull my battery and have that tested just to rule that out.
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Feb 14, 2013 | 09:59 AM
  #5  
HID's do have a large power draw (upon initial startup) that puts a load on the alternator. The more electrical power being used, causes an increase load on the engine.

Sometimes a bad ground, or weak connection can cause the issue which is why i asked for the state of your electrical system.

Some drop is normal, but not ot the point of stalling out there car. I have ZERO drop if i turn on ALL of my accessories at once
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Feb 14, 2013 | 01:44 PM
  #6  
I’ll stop at Auto Zone to test the electrical system.

Why I get whining noise in the speakers when I turn on the lights?
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Feb 14, 2013 | 03:14 PM
  #7  
Quote: I’ll stop at Auto Zone to test the electrical system.

Why I get whining noise in the speakers when I turn on the lights?
Electrical noise.

Does it rise and fall with engine RPM? Is so, it's coming from the alternator.

Have you changed anything electrical-wise with the car? Added grounding wires, or ran a power wire for anything? Amps?

Or is the car stock?

Could be a failing alternator, or a lost/corroded ground somewhere.
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Feb 14, 2013 | 05:24 PM
  #8  
I added grounding kit years ago. Last year I replace the stock stereo wand added amps in the trunk but I didn’t have these issues after the install.

Several months ago I added Motordyne spacer but I don’t recall it causing any issues with the idle RPM and noise.
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Feb 15, 2013 | 07:34 AM
  #9  
Well, that's an entirely different discussion. But since this problem is brand new, i wouldn't think that's your issue unless you just didn't notice it and it's gotten worse.

Giving electricity too many paths to ground by putting ground wires everywhere creates something called a ground loop. That can create electrical noise like you are noticing. Ideally you want ONE solid ground, vs many grounds.

But like i said, if your issue is new, i'd investigate elsewhere.

Reason why i'm dancing around on causes is because diagnosing eletrical gremlims over the internet is tough. I can really only make suggestions but really can't troubleshoot on my own. Based on what you've said, my top suspects would be a failing alternator or a grounding issue. Unless i could stick my head under the hood and start poking around, not much else I can do from here.
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Feb 17, 2013 | 10:19 AM
  #10  
Took the car yesterday to NAPA to check the charging. The guy said that everything checked ok but he said that the battery is a little bit low on charge and when the car is under load the amp is low.
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Feb 17, 2013 | 10:41 AM
  #11  
I don't know if I'd take the word of an auto parts store with issues like this. I'd want to know what's dragging down the rpms when I turn on the headlights. Either you have a wire issue in the headlight system or in fact your alternator is weak. I have a 10 wire Gordee grounding system that I installed 7 years ago, doesn't make noise or cause any issues. If you have the funds stop by Nissan and have them check this rpm drop issue out....Gary
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