Alternator problems?

[Alcomo]

Ive got a 2001 montana that is having an issue with the interior and exterior lights dimming and brightening when idling. I opened up the hood while it was idling and noticed that the belt tensioner is moving slightly. Would this affect the alternator while the vehicle is idling? Once I press on the gas and the belt spins a bit faster everything is fine.

Is the belt skipping on the alternator and causing irregular currents while idling?

[maxwedge]

Slight movement of the idler is normal, have or test the alt output to see what is happening.