Dose any one know how to test for air leaks ,it sound like its coming from the inlet manifold area iv checked the pipe work and cant find it i did have the half inlet off when i did my beiges but it was a rubber gasket that looked new ish so i didnt change it .
It didnt bother me at first but now the cars keeping the revvs on when im changing gear and at lights

any help would be appreciated
thanks paul