Juddering in low gear and at stand still

Hi I drive an 05 Clio and have recently taken it to the garage due to a juddering when I'm in first gear or driving under 20mph also car judders when I'm at a standstill. The gas is sometimes un reactive. If I rev when still the car backfires and juddering stops. When I start car after this juddering comes back. Blokes in garage have told me that it's the oxygen sensor, but asking around I've been told to clean breather pipes and throttle body. Apparently these were cleaned at the garage :/ if anyone can help I would appreciate it :).



Many thanks, Jodie