so at idle ive noticed my truck will drop about 100-200 RPM like the AC pump kicked on but the air is off so is the blower motor my lights dim for a second then the RPM goes back to normal. i poped the hood the AC is NOT spining when this happens im trying to figure out what is making my truck surge any idea?

97 F150 4.6L

 

was timing it today happens every 10-15 seconds at idle.

 

no one?

 

took a video tonight when i came home from my G/F's house kinda hard to see some of my dash lights are out but you can see the tach needle drop and you can also see the other lights dim as well. it is not the A/C pump my E-fan is off and i do not have subs in the truck. what is makning this surge?

i can see the lights flicker as i drive down the road to every so often.