52 plate Omega 2.2dti

Hi, I drove through a small bit of flooding about a week ago and immiediately after doing so the engine management light came on and the car is running really badly, reduced power, very lumpy tickover and extremely difficult to start from cold and when it does the idle is up and down and all over the place and is very smokey on start up aswell. Any ideas? Im wondering if it could be to do with the catalytic convertor as the car was running suberb before the floodwater was enterd. The light stays on continuosly after it has started but it can take five mins of eratic tickover before it starts to idle properly from cold and very smokey until it is idling correctly but the management light stays on and it wont rev well under load but revs ok when out of gear,
cheers colin