My problems with my 2003 5.3 started with the alt. quitting, I had it rebuilt & my truck has had idle issues since then, it will go down to 400 rpm's & quit at a stop light & sometimes it will quit when you let off the gas, if you are sitting at a stop light long enough the idle will come back up & it will start charging again. I have had it checked 3 times at my dealer 2 times at a local garage, I have no codes & I have cleaned the throttle body. this has been going on for over 3 thousand miles & the battery is a new battery installed by the dealer last Friday. No one knows what to do to fix my truck any ideals on what is wrong?

 

Just a wild guess.......but could your voltage regulator be going bad?

 

When the alt was rebuilt the voltage regulator was replaced as well as the brushes. My main problem is the low idle & how to fix it I have cleaned the throttle body with no improvement in idle, cleaned the mass air flow sensor with no improvement, nothing I do helps. I can't let my wife drive it because of the quitting & stumbling off the line at a red light or stop. The truck is a keeper, I just got it paid for & it only has 147000 miles on it

 

the alt and the stumbling are probably not related just coincidental. if the engine rpms fall too low the alt will not be spinning fast enough to create a charge and the light will flash on.

any check engine lights?

 

No check engine lights. Just had it checked at the dealer. It has got the best we have locally stumped

 

i would look towards the IAC

does it make a difference if the a/c is on or not?

 

It does with or without the or lights on. If I keep the RPM'S around 600 it is fine

 

i was more getting at the a/c compressor adds a little load to the engine and the iac has to open up a little more to compensate. i think your alt is probably fine. even if it was bad it shouldn't cause the engine to stumble till the battery becomes completely discharged. i would try cleaning the throttle body and iac. check for posibly any electrical connectors that might have gotten loosened when the alt was removed. and if you haven't done a basic tune up in a while it would probably be a good time.

 

Checked it this morning early when it was 58 degrees outside. With no AC on, but with headlights on it was fine idle stayed 600 or so, it never did discharge the 1st bit, I just wonder now if heat will do it the same way