2003 GMC Sierra SLE 4.8L stalling at idle


#1

My car wouldn’t start earlier this week. After jumping it, it stalled out at the first stop sign. I got a new battery and it started great but it still stalled out while idling and low rpms. I gave it a tune up in hopes that it was a bad spark plug or wiring issue. It is running better but it still gets really choppy at stops or idling at a light and it still wants to or has stalled. I had disconnected the negative charge from the battery to check if it was an alternator issue but it ran fine without the battery. Could this be a fuel filter issue or am I over looking something else? Please help!


#2

First describe the no start episode at the beginning of the week. It wouldn’t start, as in it wouldn’t crank when you turned the key?

DO NOT disconnect the battery while the engine is running. Not only is this not the way to test an alternator, but it is also a way to cause very expensive damage to the car. (http://www.troubleshooters.com/dont_disconnect_battery.htm)

If your no start was indeed a dead battery issue then the first thing I would do is have a local shop or even an auto parts store run the alternator through a proper load test. Then I’d move on to other things.

If this is a problem confined to being at idle then you’d want to check for vacuum leaks and clean your idle air control (IAC) valve.

If you have any doubts about the fuel filter, btw, why not just replace it? Its a typical maintenance item that you should never really have a question about b/c it should just get replaced on the recommended interval. A basic fuel pressure check would be wise for any problem like this, though a fuel pressure issue would be most likely to show up under load rather than at idle.


#3

when it wouldnt start, it would click but the engine wasnt igniting. I know it isnt the starter from the way it sounded when I turned the key. When it was jumped it did ran fine in park but died when i tried to slow down like at a stop light or i let off the gas pedal at a turn. Thank you for the info regarding the disconnection of a battery. This is really good to know!