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Dead Battery *and* Rough Idle


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#1 pgwerner

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Posted 12 August 2012 - 10:28 PM

So no sooner have I done some much need maintenance on my car, do I start having problems with the battery and the engine.

Last night, I notice that I couldn't get into my car via the electronic unlock, nor does the "panic" button set off the horn, and since it was a cool, damp night (basically, San Francisco Bay Area summer fog season), the battery must have died. The next morning, I call my road service to come out and jump-start my car. This works and I take it for a drive, since I want to charge the battery up and see how the car is working.

When I get to the stop sign, I notice my car is shaking *heavily*, and that this problem disappears once I start driving again. I take it around the block, noting the same behavior. Once I get it home, I look under the hood and see the entire engine rattling like a washing machine. I later restarted the car, with some trouble, and the engine was behaving the same way. The last time I tried to restart, I got a harsh "non-engage" sound, then the starter died entirely. There's a small amount of power now, enough to open windows (barely), but otherwise the battery is dead. (Battery "porthole" is totally black, even after the initial jump.)

I'm not so worried about the battery issue - I am at just about 100K, and it needs a replacing, so I'll do that. What I *am* concerned about is the engine behavior while idling - I'm presuming this is related to the electrical system and hence to the engine timing. Could this simply be a problem with the low battery, that will resolve once I have a new one, or have was there damage to the alternator (or worse) when the battery was drained or during the jump start?

I should note that I just did 100K service (mostly fluids, filters, and new tires), but more notably, took advantage of the manufacturers recall of the ECM and just had that replaced, and have since run the car under the new ECM for 1000 miles without incident. (Hence, I don't think "broken ECM" is the reason for my problems.) I also replaced a fuse for the radio and cig lighter and a dead overhead dome bulb in this round of maintenance as well, for what it's worth. (I really wish I'd thought to have my battery tested too!) The only other thing is that I have bought a new power inverter which I've been using to recharge my laptop and cell phone, but I keep it turned off when not in use, and only use it when I'm actually driving the car.

Anyway, I'm going to get the car jump started again tomorrow morning, then I'm off to get a nice Bosch Premium Power battery at Pep Boys. I'm *hoping* that fixes things, though I'm worried that the rough idle might be a bigger and more expensive problem.

#2 grim

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Posted 13 August 2012 - 08:29 AM

Could be the alternator instead of the battery, a lot of places like autozone will check it for free. Would explain dead battery and rough idle as the alternator is barely producing enough power to keep the car running at idle, it can't charge the battery.

#3 BobLevine

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Posted 19 August 2012 - 05:17 PM

When my dealer put in a new battery, disconnecting power for a few minutes caused the engine to have to "re-learn" its settings.

It was very rough for a few hours. Service tech apologized for not warning what interrupting battery power can cause.

Hope that's your issue since it fixes itself.