# Dead Battery / Rough Idle (Little Long)



## dduk (Jan 3, 2002)

So, I've got the similar rough idle problem that seems to plague the 2.5L (3.0L too?) engine. Didn't bother me all that much, just had to restart the car or rev the engine a little. But this morning (~10F) the battery was completely dead (1.5 years old) and after a successful jump, the idle was rough. After a minute the engine died and refused to restart and the SES light lit. Could be a coincidence, but been hearing noises coming from the front of the engine (kind of a very mild metal-to-metal clanging - loose belt or alternator?) when starting in cold weather as well. The dealer's replacing some of the plugs (SES was multiple engine misfires) and planning on giving it right back to me. There is no way I'm taking the car back unless they at least replace the battery or look into what was causing it to die. I'm leaning towards the alternator (but without the battery warning light, I doubt it), any ideas? I hope the VW coil pack bug isn't visiting me again . . .

BTW, Roadside Assistance was terrible and I gave them a very bad (I think option 1 was poor) rating. Wouldn't even give me a free rental or loaner. Guess it's the dealer's responsibility. I was lucky to find a dealer that would at least give me a free rental (some Chrysler POS, I can't keep them straight). Point is, I had to put in about 10 calls to arrange everything, where I thought that's what Roadside Assistance was supposed to do!


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## dduk (Jan 3, 2002)

Word from the dealer is that 2 plugs were fouled. Why they don't know. And why the engine wouldn't turn over well they don't know. Everything supposedly checked out OK. Any plugs foul on other's rough-idling cars?


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## Artslinger (Sep 2, 2002)

With late model cars after the battery fully discharges and jumped it may not run, or stall because of the high electrical loads of the newer cars. I would insist the dealer do a charging test on your car and make the car is charging properly. And if the dealer will not replace the battery under warranty, bite the bullet and spend the 60 bucks on a new battery. I would not use a recharged battery on a late model BMW especially in colder climates.


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## dduk (Jan 3, 2002)

Dealer did a full chargins system check and everything was OK. My problem is that the battery was dead before I tried starting it (Engine cranking very slowly). So I have two unanswered questions: 1) what was draining the battery and 2) what is causing the fouled plugs?


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## RKT BMR (Sep 7, 2002)

Artslinger said:


> *With late model cars after the battery fully discharges and jumped it may not run, or stall because of the high electrical loads of the newer cars.*


???

This makes no sense. It implies that the alternator is not capable of producing sufficient electrical power to run the car, in which case the extra current would come from the battery, and it would drain rather than charge when you are running the motor. We would all be needing jumps regularly.

Quite the contrary, the alternator has more than enough capacity to run the motor and most of the power-hungry electrical accessories (headlights, climate blower, radio) with sufficient capacity left over to charge the battery.

However the _battery_ generally does not have the current capacity to turn over the starter with all these things on. I think you got this backwards.


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## Artslinger (Sep 2, 2002)

RKT BMR said:


> *???
> 
> This makes no sense. It implies that the alternator is not capable of producing sufficient electrical power to run the car, in which case the extra current would come from the battery, and it would drain rather than charge when you are running the motor. We would all be needing jumps regularly.
> 
> ...


Are you sure of this? I'm talking about a battery that will not hold charge. If you are saying I was incorrect with my statement, which came from an actual mechanic, do you have any thing to support your statements. And I stand by my statement that using a recharged battery in below freezing temperature zones is not a good idea.


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## Marco (Mar 7, 2003)

*of dead batteries*

I am confused and frustrated:
I live in New England. Both my cars are parked in unheated garages. After, say, four days without using them, if the temperature has been below freezing, both cars have flat batteries. By now they are both ruined, I am sure.
I hope that this will not happens when I get my new BMW. Or will it?
Is cold weather unavoidably killing batteries?


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## dduk (Jan 3, 2002)

*Re: of dead batteries*



Marco said:


> *I am confused and frustrated:
> I live in New England. Both my cars are parked in unheated garages. After, say, four days without using them, if the temperature has been below freezing, both cars have flat batteries. By now they are both ruined, I am sure.
> I hope that this will not happens when I get my new BMW. Or will it?
> Is cold weather unavoidably killing batteries?  *


What's frustrating is that it was only sitting one day without use, and wasn't that cold out (10F). All the eletronics do consume a finite amount of current even in sleep mode, but it shouldn't be enough to short a battery overnight, in any weather.

I'm starting to think I have other problems. Anyone with a MT notice that when depressing the clutch and letting the engine rpm's fall, that they fall below 500 rpm and then jump back up to 700 rpm? Perhaps that's where my plugs are fouling . . .


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## Artslinger (Sep 2, 2002)

*Re: of dead batteries*



Marco said:


> *I am confused and frustrated:
> I live in New England. Both my cars are parked in unheated garages. After, say, four days without using them, if the temperature has been below freezing, both cars have flat batteries. By now they are both ruined, I am sure.
> I hope that this will not happens when I get my new BMW. Or will it?
> Is cold weather unavoidably killing batteries?  *


The car's alternator is not designed to fully restore a depleted battery, it maintains the charge on a good battery.

A battery charger needs a day or two to fully charge a battery.

If your car sits in cold weather 4 or more days without running, you may want to use a battery trickle-charger.


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