Question about 2002 Ford Expedition

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Idles low when ac/heat is on and lights dim

Idles low(600) when ac/heat is on and headlights dim. recently replaced alternator(was doing this before replacement). voltage is at 15 with lights on but drops to 13-12 when blower at full blast. when i lower the blower speed the voltage rises. also when i speed up rpms. when it is idling low say at a stop light you can hear the blower speed slow down then pick up when you drive off.( rpm increase)

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Fix the idle speed to 850-900 rpm
check the alternator and voltage regulator as the voltage should read 14.5-14.8 volts dc at 1000rpm or higher regardless of what is running
have it bench tested by an accredited auto electrician

Posted on Aug 04, 2017


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SOURCE: 2004 Ford Ranger Low Idle

I figured out what was going on. supposedly on ford rangers the Idle Air Control Valve (IAC Valve) goes bad. i got a trouble code looked it up and sure enough it is the IAC Valve. Under 100 bucks for the part

Posted on Jul 13, 2008

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SOURCE: gmc sonoma voltage fluxuation & headlights dim at night

I would still have the alternator chk. sounds to me that the internal regulator or a diod is going bad.

Posted on Mar 04, 2009

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SOURCE: lights and fan blower motor speed decreases when idle steady

vachum modultor motor is leaking.

Posted on Jul 22, 2009

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SOURCE: Dim Headlights. 2001 Jeep

seems like a power issue, you could try buying a new battery or take it to an autozone and have your voltage checked battery should be putting out near 13 volts.

Posted on Aug 11, 2009

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SOURCE: 2000 Ranger 4.0 Automatic 4x4 will not idle up at

the idle air control could be faulty.

Posted on Dec 13, 2009

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2006 Cadillac CTS help My car was tested @auto zone for the batery n alternator n both passed Good voltage Everytime I go to crank my car it does not crank I have 2 jump it of even if it's for 15 mins

Luis: That makes no sense. But here is what others are saying: " How possible is it for a bad alternator to be tested good? I already had people telling me to replace it.

I got both the battery and alt tested. Both passed.

Reinstalled on the car and it ran good surprisingly after the battery was charged @ the autostore > till after about 10 minutes, then the battery meter dropped back down.

Soon as i turned on the lights/ac the battery meter dripped down real low. SOon as i turned them off the meter jumped back up.

Soon as i revved the engine the headlight would brighten then dim back down after the rev was over.

I can jump the car, but it will turn off by itself if you leave it idling to long then it needs another jump.
Driving it doesn't charge the battery up.. its actually drops the battery meter down more and more and more till its dead.

-Car doesn't drain the battery while its off.. so its nothing left on.

>> Now people are telling me there alternator was tested good, but the problems went away after buying a new alt.
Some people say there could be a loose belt not turning the alternator fast enough to supply power to lights/ac and charge battery. Or bad wires". or possibly a bad voltage regulator.

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Left headlights

Check your connections at the wiring harness going to headlights for corrosion, sounds like high resistance somewhere, also make sure your ground wires are secure. It wouldn't be the alternator or the battery would be dead and not start the engine. Also shouldn't be any condensation in your head light assembly's or will cause bulbs to blow prematurely.

Feb 22, 2014 | 2002 Subaru Outback

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I have a 99 solara se. I have new battery and alternator but the car can't carry a load. Ac lights heater radio so forth

Not sure I follow your problem.
The alternator puts out 13-14 volts at idle but very few amps. If you turn on the headlights at idle the voltage may drop to 12 until you raise engine speed. The amperage goes up with engine speed.
Is the battery voltage at least 14 when the engine speed is 1500RPM or more ?

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I have a 2005 chevrolet silverado my dashlights and headlights are strobing how do i fix them?

Are you having problems with headlights or interior lights flickering or dimming for no apparent reason? You are not alone! Many other consumers have reported experiencing the exact same problem. The problem is seen in many different GM makes and models including, but not limited to: Chevy Suburban, Tahoe, Silverado, Corvette, Camaro, Firebird and Malibu's and Pontiac Aztek's.
Why Are My Headlights Flickering?The headlight flickering or dimming may be caused by a intermittent low voltage output from engine vibrations. When this occurs, a voltage spike causes the voltage regulator to reset. During the reset, generator output drops to almost zero. This is a known issue with GM cars and the correction involves replacing the alternator. Would recommend seeing dealer for proper alternator application to resolve concerns. Probably has a superceded part number to indicate internal changes.

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Check the cable connections to the battery. If they are loose or dirty, clean them and tighten them. Check the battery for water while you are at it.

If that is okay, have an auto parts store check your charging system - they do it for free. You could be in the early stages of alternator failure or diode failure.

I had a van that did this for years but was always leery of it.

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