Okay, this is on a b17 EF, havent driven it in about 9 months, here are the symptoms:

*jumped the car due to dead battery*

1) car wants to die at low rpms (even if Im going 50mph).

2) if the car is idling, it will shut off when I try to turn on the head lights.

I have a fair guess of what it is, but just want to hear you guys' opinion first.

 

hrm.. im thinking maybe the alternator? (but im probably wrong...)
whats your opinion?

 

Doesn't sound like you let the battery charge long enough. Could be the altenator, old fuel, dead battery, etc...

 

Did you start driving right away after jump starting it?

The ECU needs to relearn the idle parameters after it loses power. I once replaced a battery and drove off right away. Car stalled at every stop. Reset the ECU and start the engine and let it idle up to operating temp without touching the gas pedal.

 

no, I waited a minute before driving it.

yeah, I think it may be the alternator. Whats the best way to check this? Im guessing w/ a multimeter at the battery terminals during idle?

 

The easy way to check it (be careful when doing this) is to start the car with the negative battery terminal loose, then disconnect the battery while the car is running, odds are if it shuts off, the alternator is not charging/keeping the car alive.

 

I think the alternator is still strong enough to keep the car alive at most times, its just that when I load it w/ more duties i.e by turning on the headlights, that the car shuts off.

 

if you took it for a good 20 min drive on the freeway the batt should be good.

your car sat for 9 months? check for corrosion on the battery terminals and the alternator.

 

Well even if the battery is working it could still have a bad cell and that would not allow anything to work properly. So spend the $50 bucks and buy a new battery

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the DR. &raquo;</TD></TR><TR><TD CLASS="quote">The easy way to check it (be careful when doing this) is to start the car with the negative battery terminal loose, then disconnect the battery while the car is running, odds are if it shuts off, the alternator is not charging/keeping the car alive.</TD></TR></TABLE>

Even if you do this it wont matter ,because your car is not a 1972 with an generator with continuing amount of power, but it has an alternator with an alternating current which could make the car shut off.