I was wondering if a weak battery would cause low idle? I let my car sit for 2 wks because i was away at school. I left the battery connected and it drained. But it started right up when i used jumper cables. i then drove my car around to charge the battery. It started fine and had power the next day but my idle has been low kinda around 500-600 ish. Been like that for a while. Car is a 2000 civic SI. I wouldn't think it's my altenator because it charged my battery and it had power afterwards. When i let off my throttle, my lights do dim and rpm is around 500. But i do have the radio on with my lights and fogs.

 

Could be a battery or the alternator. You need to take the battery and put it on a real charger overnight. Using the alternator to charge the battery puts too much stress on it and takes too long to try and bring it back to 100%. If the battery has a dead cell or a short it will give the impression of a bad alternator.

Charge the battery, have it tested.

 

i dont think its ur battery or alternator. bad alternator will cause your rpm and speedometer and stereo to jump around and go crazy. a bad battery will make your car have trouble starting and have a weak crank. ithink.. i had a bad alternator and bad battery couple times and those were the effects on my car.. so yeaa correct me if im wrong.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EM1_ChRiS &raquo;</TD></TR><TR><TD CLASS="quote">When i let off my throttle, my lights do dim and rpm is around 500. But i do have the radio on with my lights and fogs.</TD></TR></TABLE>

Your batter probably just isn't fully charged. Do you know how to use a voltmeter? You can check your battery yourself.
After your batter has been FULLY drained, you should get your battery recharged at a local shop (most places even do it for free and it takes an hour or two) as driving it around and relying on the alternator to do all the work isn't the most efficient way to charge a battery from 0% to 100%.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ph0shizzle &raquo;</TD></TR><TR><TD CLASS="quote">i dont think its ur battery or alternator. bad alternator will cause your rpm and speedometer and stereo to jump around and go crazy. a bad battery will make your car have trouble starting and have a weak crank. ithink.. i had a bad alternator and bad battery couple times and those were the effects on my car.. so yeaa correct me if im wrong. </TD></TR></TABLE>

Your wrong. There are 100's of symptoms of a failing battery or alternator, I doubt you have seen them all so don't discount something because it hasn't happened to you.

 

There are 100's of symptoms of a failing battery or alternator


What are they??