when the truck is in park, the RPM's will bounce from 600 to 900 rpm's... also i hear a clicking, like the fan is turning on and off.

 

Is it your fan?

 

dunno, never bothered to get out and check...

 

defroster on?? sounds like ac compressor

 

compressor relay gone bad maybe?

tune?

EDIT: ahh, you beat me by a few seconds there.

 

As far as the tune goes, there is logic programmed to increase idle speed if the ac compressor is on. If it is in fact cycling on/off then that is most likely the reason for the rpm variation.

 

a/c isnt on, but the defroster is, but on heat.... i'll turn everything off and see what happens..

 

Is it happeneing real quick, kinda like a lope, but hard and quick.

 

Just an FYI - the A/C compressor goes on when the defroster is running even on high heat. The compressor de-humidifies the air so you don't fog up. So your idle issue is caused by the A/C compressor which triggers higher idle rpms in the PCM.

 

could have a short cycling compressor due to a low a/c charge
Tex is right on.