Corsa c 1.2 sxi - Engine or accelerator problem - treborbd81

I have just bought a corsa c 1.2 sxi.All seems well at first when engine is just tickin over but when i slowly start to push the accelerator the revs start to wave up and down. then when i increase revs further to around 3000 and hold it still it carries on revving??.Acceleration when driving feels sluggish then the next minute it seems ok.

Please can someone help me with this.??

Cheers