My 2001 1.8 tddi estate began idling rough and blowing blue smoke at startup. The smoke increased with the revs and only cleared after a short drive. Was going to book in for a diagnostic, but first decided to try a few things, namely; changed the air filter element. Cleaned the EGR valve in situ using Wynn's carb and air intake cleaner (saw Youtube video on how to do this). Changed the oil and filter. Disconnected the negative battery lead for 10 minutes to reset the computer. Idle and blue smoke problem solved.