fast idling and mis firing 3cyclinders corsa sxi 1.2 53plate?

yes my gf is having problems with fast idlingand sluggish driving also sounding like firing on 3cyclinders and car had throttlebody replaced few months back when it was doing more of the same thing but the oppisite way around,,my friend who used be mechanic said idle throttle sticking or crank rod sensor needs replacing could you advise of the problem thanks and does need new plugs and leads?