Got an 03 manual and i have been noticing that when i start it in the morning or if i go to dinner and come out if i sit there for a few min to let it warm up i can hear the idle change. It kinda makes the sound of when ur ac pump kicks on and off and the idle changes. But i have nothing turned on no heater or head lights. i only have 50,000 miles on the truck and ideas what it could be?
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I'd be willing to bet it is your grid heater. It will put a pretty good load on your alternator when it cycles off and on. Turn on your headlights and see if they dim when you notice the change. If they do, that's what it is.

 

Most likely intake air heaters turning on and off. They put a few hundred amp draw on battery's which causes alternator to charge battery at higher rate. This will load the engine causing rpm's to fluctuate slightly until engine warms up.

 

that makes sense now temp up here has dropped just never noticed it before. didnt mean to put this thread in the 07 and up.. but thanks guys