Battery Question....
 

Hey Guys/Gals,
I'm a newbie so I first want to say hello...hello!
Secondly, I have an issue. I left an interior light on over the christmas break and when I can back the battery was dead. I got a jump which worked but when I went to start it the next day, no dice. I then purchased a new battery from Struass, she started right up. The problem is when I stop at a light the car makes a wierd struggling noise. It idles really low like it's going to cut-out and then rev's a little. it does this 3 times and then seems to be fine. If I slide the car into neutral before I stop then it doesn't do it. Could this be the alternator? Is there some kind of new fangled gadget that electronically control what your idle is and when I lost all power it needs to be reset? As you can see I know almost nothing about cars but if it's something simple I can try to fix on my own.
In any event, I look forward to any insight you might have.
Thanks in advance
P.S. don't know if it makes a difference but there was dried up blue foam all over the battery contacts before I changed the battery. I cleaned the wiring harness off as much as I could with a wire brush...

It doesn't sound like an alternator issue to me.

The total loss of power will sometimes cause stuff to need resetting in your computer, and that sounds like what you are experiencing. I'm not sure how long it normally takes for it to reset, though - hopefully somebody with more Mazda ownership experience will chime in shortly.

If your cable ends still have residue from the corrosion, that will keep you from getting an optimal electical connection. I don't know to what degree, if any, it may contribute to the symptoms. I understand there are some chemicals for cleaning that stuff up real well (my son is a Lexus technician), so you might ask about it at the auto parts store.

Good luck! Please keep us posted on the outcome. We're all in this together!

What kind of car do you have, and how many miles are on it?

To reset the ECU on a 3rd gen Protege (protege5, MSP, etc):
Unplug the battery, pump the brakes a few times to drain any charge out of the system, wait 5-10 min, plug the battery back in, start the car, and let it idle for 5 min or so. The ECU will relearn everything while the car idles.
If that doesn't fix the problem, I'd probably start at the 02 sensor.


The blue stuff was just a little battery acid. The easiest way to clean it (before it gets on anything and begins to oxidize(!)), pour some baking soda and water on it, then wipe it with a brush or rag. Be careful if your brush is steel, it's a battery full of electricity!

HA! I don't know why I assumed everyone knows what kind of car I drive....it's a 2005 MAZDA3 2.3 hatchback with roughly 85k. Will Def try what you suggest, eggnatey.
I have done a little reading and it appears I am not alone. Others seem to have had luck with cleaning the throttle body. It makes sense that there is buildup of gunk that may cause the fluctuation, does that make sense? The battery dying may just be a contributing factor. The real cause of the rough idle is because the battery died I left it for a week untouched, thus letting the gunk build up and freeze? Anyway the process seems relatively easy and even a car idiot, such as myself, can do this without breaking anything (hopefully). I will update the post if this resolves anything but any more suggestions will be greatly appreciated!
Thanks again!