audi a3 not revving above 2

hi I have an audi3 1.8 2001. it was running fine and all of a sudden my gas was guzzled and my power slowed to 50mph. took to garage and diagnostic said 02 sensor and cam sensor. the belt had jumped 2 so was replaced and set. cam sensor was changed. however still not going over 2 revs. all pipes have been cleaned and checked. new plugs placed and compression test is fine. however my car still has no power. any suggestions please.:runaround: