Why does my fiat stilo 1.6 loose power?

I have a fiat stilo, 1.6, 2003. When sitting idle the revs go very low and it nearly cuts out, when I start to move, it doesnt seem to have the power, then all of a sudden it does gain power and jerks forward. Also, when travelling slowly in traffic at veryh slow speed in 2nd or 3rd gear, the car can not cope and chugs and jumps.