Idle speed

Is there any way to adjust the idle speed? My truck idles at about 500 rpm which doesn't seem to keep the alternator spinning fast enough....dash lights dim, head lights dim, a/c and/or fan
speed decrease, etc. However, if i run the rpm up to about 600 - with my foot on the brake - the volt meter jumps back up where it should be...about 14 volts. i have a 5.3 V8 OBS '99 Silverado Z71.
any suggestions?
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My guess is the battery or alternator is weak. I've a '99 K1500 with the 5.7 liter and the idle is at 500 rpm when at operating temperature. The lights, etc. are all stable at idle on mine.
Brian
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i doubt it is the battery.....its 5 month old optima red top. i may have too small a pulley on the alternator. i changed the under drive pulley and when i did that i put a smaller alternator pulley. i guess i try and change the pulley back to its original size and see if that works...sure is a whole lot cheaper than a new battery or alternator.

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Texas Legend wrote:

Smaller pully means the Alternetor is Spinning Faster At IDLE..and more output!
I am with The other Person, YOUR BATTERY IS WEAK. Even tho it is almost NEW.. You may Have Cooked it with a Bad Alterator/ Regulator !!
i guess i try and change the

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What is the underdrive pulley?
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crankshaft pulley....sorry. theory is you gain horsepower because its less work on the motor to drive a/c, alternator, water pump, etc. think of it like a sprocket on a bike. if the chain is on the small pulley (chain ring/sprocket) in front and larger pulley (chain ring/sprocket) on the back it is real easy to pedal...but you don't go as fast. hence the reason i thought this might be the reason for my alternator not spinning fast enough.

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It probably is the reason. You put a smaller pulley on the crankshaft to turn the accesories with less effort. And you had to put a smaller pulley on the alternator to bring it back up to speed. If you didn't have the dimming problem before the pulley change, I bet that the combo of pulleys you put on the crank and alternator doesn't match the pulley ratio of the stock set. You can check this by measuring the diameters of all four pulleys (the stock pair and the new pair). Divide the diameter of the stock crank pulley by the diameter of the stock alternator pulley. If this number is bigger than the same number for the new set, then your alternator is turning slower than stock and this would explain the dimming. There are five courses of action:
1) Put up with the annoyance of dim lights at idle as a tradeoff for a few extra horses 2) Turn up the idle RPM, if you can do it without screwing anything else up 3) Put an even smaller pulley on the alternator 4) Put an slightly larger pulley on the crank 5) Go back to your stock pulleys
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be...about
If a 100 rpm gets it back to being right, its easy enough to adjust. The adjustment screw is a very tiny torx that is difficult to find. The head faces down toward the intake. Standing at the front of the truck, look at the throttle lever. It has the cables attached for the gas feed. The adjustment screw is to your right side and you can't see it. These trucks are famous for getting carbon buildup in the throttle plate which causes slight accelerator sticking. I jacked my idle about a 100 with no problem.
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