what causes this? my car has an erratic idle and revs up and down. When I pushed in the clutch today while it was going up and down you can hear a whining noise but as soon as you let go of the clutch it goes away? is it the throwout bearing?

 

probably

 

I had the same problem on a Mazda I had once. The noise turned out to be the throwout bearing. The clutch was also on its way out at the time.