Most likely throttle related,not clutch and in the throttle area it is actually more likely the carburetor than the cable,These Hitachi carburettors are all quite old these days and you will find wear in the lower body of the carburettor where the throttle shaft runs these can be a pain to strip as the round butterfly plate has to be unbolted and the 2 screws are quite tight and will take some effort to remove then you need to have new bushes machined up to fix the wear.
Any wear here results in uncontrolled air leaks resulting in a higher than normal idle and it will also vary as the butterfly valve (throttle plate) never seats correctly every time and therefore sometimes it idles OK other times too fast and doesn't idle smoothly and is never consistent.