Lights Dimming and Rough Idle

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My '06 corolla is having some issues. at idle, when i turn defrost on the lights noticeably dim and get brighter when I turn it off. Happens when I lug the engine as well. Sometimes it takes like 6 or 7 cranks to start up and other times it will start almost instantly. Also has a rough idle that seems to hunt between 600 and 1000. Battery voltage with car off is 12.57 and voltage with car running is 14.1. Any ideas before I go on a wild goose chase with money I don't have?
 
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BrandonVA

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14.04 with defroster on. not sure how old the battery is. bought it used a few weeks ago. looked for a date on the battery but couldn't find one. don't have a hydrometer. not sure what that is. I checked it with a multimeter.
 

BrandonVA

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told my dad about it and he proceeded to turn his car on and it does the same thing...hmmm. i'm sure his battery is old as [censored]. never noticed any of my other cars doing this.
 
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Many alternators can't put out rated power at idle. It's normal to see the lights dim with a heavy load. They should brighten as the RPM's come up. It'll be more pronounced with a weak battery.
 

Nick1994

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Sounds pretty normal, my 97' Camry did this at idle and even the dash clock would dim at idle LOL until I revved it or drove off from the light.
 
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Most any auto parts store will check your battery and charging system for free.
 

CT8

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Why is the engine idle changing? if you hold the throttle at a 1000 rpm what happens?.
 

Bud_One

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Originally Posted By: BrandonVA
no light. i think it may be a leaky intake gasket causing my idle to drop.
That's what I was going to ask next. If you had replaced the intake gasket with the updated orange OEM type.
 
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Originally Posted By: Nick1994
Sounds pretty normal, my 97' Camry did this at idle and even the dash clock would dim at idle LOL until I revved it or drove off from the light.
None of my vehicles lights dim at idle, nor do any of my vehicles exhibit a rough idle. I would disagree that it's normal.
 
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some cars actually boost idle speed when voltage drops badly to get around the dimming at idle a little, but not all. Been a regular item with vehicles since before the alternator. all depends on the vehicle and the amount of loads in play. don't know what is "normal" for that specific corolla, but it is not anything I would consider a problem unless there were other odd symptoms, flickering at idle, battery remaining undercharged as evidenced by harder starts than is regular for that car, etc..
 
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also, a lot of cars do get dimmer at idle, but it is not immediate--- very gradual as the V gently drops. It used to be obvious because sudden acceleration would quickly raise the voltage and you'd hear it in the A/C fan. However, that is harder to detect now as some vehicles delay the immediate output increase from the alternator for a number of reasons--- alt life, belt life, reducing engine load during acceleration. Those changes also make it much less obvious.
 
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yep, our fleet GM vehicles will wait a few seconds and then smoothly and slowly raise the idle a bit until the voltage comes up. Most folks will never even notice it...
 
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Originally Posted By: Pop_Rivit
Originally Posted By: Nick1994
Sounds pretty normal, my 97' Camry did this at idle and even the dash clock would dim at idle LOL until I revved it or drove off from the light.
None of my vehicles lights dim at idle, nor do any of my vehicles exhibit a rough idle. I would disagree that it's normal.
Just because your stellar fleet of peach automobiles don't do it doesn't mean it isn't normal. I guess even your cars are perfect and without fault,just like you there pop. Anyways this is very common in higher mileage or older vehicles. All my work vans do it,my charger does it though it's only perceptible when its -35c or colder and all the accessories including the heated seats and the DVD player are on. My 99 silverado dims the dash lights slightly at a stop and do does my c3,so yep. Normal. None of my examples have battery charging problems. They crank easily at -20c when I went out last night. I think its just older wiring,grounds getting light corrosion on them. Adding a couple of grounds may help,and not costly to try.
 
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Those voltages are good, but that does not tell the whole story. A battery can have good voltages but 1/2 or less the capacity as it gets old. Just how old is your battery? Removing, burnishing, replacing and coating vehicle grounds with silicone (the setting kind, not the stay-greasy kind) should be done every few years anyway, particularly in any Rust Belt area like VA. A lot of salt was used in VA last Winter. It could also be a vacuum leak, such as a loose or cracked vacuum hose or the intake manifold as previously mentioned. These leads to a weak engine at idle but if the leak is small the engine is "strong enough" when given throttle.
 

BrandonVA

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i have heard of people doing ground upgrades on their corollas. Apparently this resolves a lot of issues like this. Can I just buy another ground cable and attach it to the negative of the battery to frame of car somewhere? replaced the intake gasket today. idle is a bit smoother but lights still dim.
 
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JHZR2

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Corolla wiring isn't great. A friends vibe did this, and it was so bad that the horn couldn't even maintain constant pitch. I've seen some light fluctuation at idle when battery impedance a start to grow, and so energy can't flow quite as fast...
 
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