engine tapping, lumpy idle! PLZ HELP!!

[NATHAN182]

hi, car has a slight tapping noise on idle that comes and goes. you rev it up and it goes away then 20-30 seconds later comes back.
can only seem to hear it inside the car but sound like its coming from outside behind pedals or engine, defo the o/s tho.
also the car is very lumpy and hesitant on idle and think this may be linked.
i have my suspicions thats its something to do with the 'carbon canister' or something. but dont know how this works and if it would cause this.
any help will be HUGELY apprieciated

 

[Nick-182]

Sounds like dephaser to me. Im no expert, but search the forum and you'll see loads of threads with the same symptoms

 

[NATHAN182]

cant here it from outside tho and comes and goes? anyone know anything about the carbon cannister?
hope its not dephaser

 

[NATHAN182]

doesnt sound like the dephaser, cars only got 25k on it. how long do dephasers normally last and would the sound not be there all the time