ses light on & surging idle

The SES light is on and I am getting a surging idle. It surges from 600rpm to 1000rpm. It is about undrivable. Any ideas?

Also what is a decent OBD-2 scanner to purchase. Walmart has one for $100 that looks just like one I've used before, but not sure of model. Suggestions?

Thanks
Jeremy

2002 Envoy XL 4x4 54,000 miles