i had this problem, it turned out the be the linkage cables. They must have been worn or something. Dont take my word for it though. Without seeing it i wouldn't be able to say. It could be your clutch
ye these are worth an absolute fortune, a friend of mine imports jap cars and they often come in with enkei wheels on. I can have a pop through to his unit and see if hes got owt for you if you like
Let me know mate