Hey guys. I've got a 2002 GMC Yukon with the 5.3 and am having a little problem. Whenever my AC is on, I have a serious voltage drop, down to around 12v when sitting still. When the RPM's are above 500, it raises up to 14.4v. My truck now sits right at 400 rpm's. Is this too low? It also has voltage drop ANY time the rpm is at 400, even without the AC on sometimes. If I am crusing and slow down, it will temporary drop down to 12v and raise back up. I'm going to assume this isn't normal? What do you guys recommend?

 

Do you have an UDP. If so that will cause the low RPM voltage to drop until you are off idle. Sitting at a stop sign or red lite the voltage will drop, but as soon as you move off it will pick up to the 14 volt range. If you don't have an UDP this is not normal.

 

mine moves below 14 at idle too so i am curious why this is as well

 

Also, 400 rpm is too low, even the stock setting is around 575...has the PCM been tuned? I'd recommend raising the idle if you have access to tuning software, and cleaning the throttle body as a maintenance item. A gummed up throttle body/IAC passages will affect the engine's idle characteristics.

 

Truck is 100% stock and unmodified except for a k&n dropin filter. Has been doing it for a while now, even before the k&n filter. It does it horribly bad when the AC is on. Thought it might be the plugs/wires, so I changed them out and still no luck. Will clean the TB and see if that helps. I do not have access to tuning software, so that's a no go... Mine is the flex-fuel vehicle if that makes a difference?

 

Maybe the alternator is going bad

 

clean your throttle body!!!!!

 

So you haven't lowered the idle yourself? Yeah...2002... clean the IAC or get a new one. That's my new thing. Budhayes is SO right, the IAC can really put a hurtin on your idle. Below 500 and I am surprised you even have 12 volts.

 

Well, I did the "big 3" today and cleaned my TB the best I could without removing it from the truck. I haven't messed with the IAC at all. I thought it was doing great the first 5 mins, but after that, it started the same thing all over again.

 

what's IAC stand for