Have you found out the problem ? i had exactly the same thing, Did a diagnostic check and nothing appeared, Replaced Rotar arm, and it improved, Replaced Dizzy cap and it improved even more, replaced spark plugs and it improved more too, still had a problem until 2 weeks ago one of my intercooler pipes had popped off, since then i havnt had no juddering, so i can only assume that was the problem, boost leak...