How can I fix my corsa diesel 1.7 di?

The above car recently started to have running probs.
ie, when changing up/down gears, say at junctions/r'bouts, car is hesitant briefly on pressing accelerator, bluish/grey smoke from exhaust, car then runs fine.
Occ on slight/steep hills car will struggle, and sometimes black smoke will appear, then oomph, away it goes normal.
Very intermittent prob, noticed 2 fault lights, p3080 relay glowplugs, p0407 clutch sensor, changed air flow meter, had diagnostic done, no codes shown, EGR Valve cleaned very bunged up, waiting on new relay.when car playing up feels like driving on porridge, 4 flat tyres etc , then away it goes perfect, problem becoming more prevelant. Recently drove to SE England 510 mls, perfect there and back but had put diesel treatment in tank before journey. any ideas Not using water, oil, does sometimes guzzle diesel when black smoke, had recent service not glow plugs.

Danny
September 2010