Idle surge and sticky revs

Okay, so my Mazda Bravo has been a small project i have been working on as my first car, and since we have had it it has had a small idle problem. when randomly the revs will drift up to around 1,500 then drop down again, as well as it has what i would describe as a sticky rev, so the revs don't go down as soon as my foot is on the pedal, they stay up for a bit then go down. work we have done on the car so far has been,
a head replacement, new radiator, thermostat, water pump and a new camshaft,
from my research i think it could either be the fuel filter or a vacuum leak. but i need some more mechanically minded people to help identify the issue.