Not necessarily a dead battery. Since it's new it should be strong enough to run the fuel pump, head lights, and ignition system for a good hour or longer before it runs dead. I wouldn't be concerned about the idle speed just yet until the charging system is working. There's a number of computers on the truck that will do weird things when the system voltage is low. The same is true of the radio. You might be able to prove that by running the engine while a battery charger is connected and set on a low setting but keep in mind a working generator puts out a three phase output which is very steady with low ripple. A battery charger puts out a pulsing DC voltage that varies from 0 to about 18 volts 120 times per second. That too might affect some computers.
Another cause of high idle is a vacuum leak. GM has had a lot of trouble with leaking intake manifold gaskets but they usually leak coolant. Also, I think that became a problem after '93 models.
If something is not turning off with the ignition switch that allows the windows to still work, there should be other things on that circuit that also still work. That might include the radio, heater fan, or dash cluster.
Wednesday, March 2nd, 2011 AT 6:45 AM