The idle of my car drops very low when i either rev up the car and let the revs drop or whenever i drive and push in the clutch so i can coast to a light. Idle revs are about 900 rpm and the idle drops to about 500 or less whenever i have the problem. The lights also dim when it reaches below 600 rpm. When the car finally stops, the rpms slowly climb back to normal and its fine. car is a y8/z6 vitara setup w/ y8 intake mani. 5 speed

 

mine was the alternator, the belt was a bit loose

 

I had the alternator and battery checked and they turned out to be fine.

 

all grounds were upgraded to 1/0 and the positive from the alt also.

 

Is the CEL ON? My first impression is a problem with the IACV. Have you tried cleaning it and the throttle body?